7 Organometallic chemistry the transition metals By G. R. STEPHENSON School of Chemical Sciences University of East Anglia Norwich UK NR4 7TJ 1 Synthetic chemistry by catalytic procedures This year the Report begins with a survey of the most important catalytic procedures that employ transition metals to build skeletal bonds. Because of the constraints on space minor (or new but relatively untried) catalysis systems have been omitted from this section as have catalytic procedures that e§ect functional group transformations such as oxidations and reductions. For organic synthesis it is widely applicable catalytic methods that form important bonds which merit the focus of attention. In Section 3 however mechanistic studies of catalytic cycles and more unusual catalytic procedures are discussed.Metal catalysed allylic displacements Palladium allyls in synthesis asymmetric modifications Studies of the induction of asymmetry in palladium catalysed substitution in the 1,3-diphenylallyl system continue to be the main focus of attention. An ever wider range of ligands is under investigation. Phosphine (e.g. 1)1 and diphosphinite (e.g. 2)2 ligands employ only phosphorus but mixed combinations such as P,N (3,3 4,4 5,5 6,6 or 7,7) or P,S (8,8) are now more popular. Some lack phosphorus altogether.9,10 In most cases the ee of the product is variable depending on nucleophile conditions or the nature of additives and although results in the high 90% range are possible there N O PPh 3 P Me Ph Me 1 O O O Ph O Ar2P O OPh PAr2 2 P N Me Ph P N Me Ph 4 Royal Society of Chemistry–Annual Reports–Book B 197 CpFe N P P Ph o-MeOC6H4 o-MeOC6H4 Ph 5 PPh2 Me N N Me Ph H 6 Fe PPh2 N Pri N Pri 7 Ph2P S O AcO AcO OAc OAc 8 Ph2P N N 9 NH O NH O PPh2 PPh2 12 N S N O Me Ph 10 Me N N P P ( ) n ( ) n Me 11 Ph Ph n = 2–6 is not yet a single system which stands clear of the rest in terms of generality of application.There have been attempts to step back to first principles in ligand design,11 while in other cases more elaborate macrocyclic structures have increased the numbers of ligand sites and are structurally more complex as in the N,N,P,P example 11.12 An N,N,P,P structure 12 with more degrees of freedom has been employed with cyclopentenyl acetate.13 The naphthyl analogue has also been examined.14 Ligands of this type have also been used with intramolecular allylic substitution as in the case that forms 13 (Scheme 1).15 Cyclisation of 14 with the ligand 15 proceeds in 87% ee.16 Cyano esters17 and amine18 nucleophiles have been used.An elaborate biferrocene- 198 G.R. Stephenson MeO NH OAc MeO N 13 97% yield; 91% ee i H Scheme 1 Reagents i 12 [(C 3 H 5 )PdCl] 2 Et 3 N O O Ph O O Ph O 16 O O Ph O N (–) N N N Cl NH HN O O PPh2 Ph2P Ph Ph N N N N Cl H 17 i Scheme 2 Reagents i (dba) 3 Pd 2 ·CHCl 3 MeO2C CO2Me OCO2Me 14 Ph2P N O Ph 15 based catalyst with an unusual Rh–Pd two-component system has been tried in the cyano ester case.17 These asymmetric allylation procedures are finding application in synthesis as in routes by Trost to (])-polyoxamic acid with 12,19 or vigabatrin,20 which uses the naphthalene analogue Williams’ route to b-amino acids,21 or a synthesis of carbocyclic nucleosides by Crimmins and King.22 Variants on the allylic substitution include a reduction mediated by formic acid,23 and the use of chiral palladium catalysts for asymmetric elimination reactions in mono-24 and bi-cyclic25 frameworks.Finally a prochiral substrate 16 with a variant on 12 gives enantioselective access to nucleosides with asymmetric induction at the stage that displaces the leaving group (Scheme 2).26 A similar approach a§ords carbovir using 18 as the nucleophile.27 Other palladium catalysed allylic displacements Turning aside from chiral ligands the main impression from the 1996 literature is that attention is focusing on particular classes of nucleophiles. The use of 17 (discussed above) and 18 is typical. The nucleophile 19 leads to azapurine analogues of the 199 Organometallic chemistry the transition metals MeO2C MeO2C SnBn3 + O MeO2C MeO2C OH Bu3Sn OH MeO2C CO2Me i ii 20 Scheme 3 Reagents i Pd(MeCN) 2 Cl 2 Pd(cod)Cl 2 Pd 2 (dba) 3 ·dba or Pd(bipy)Cl 2 ; ii Pd(PPh 3 ) 4 Pd(dba)(dppf) Pd(dba)(PPh 3 ) 2 or Pd(dba)(AsPh 3 ) 2 N N N N NCONPh2 NHAc H 18 N N N N N NH2 H 19 natural structures.28 Carbocyclic nucleoside analogues have been accessed using 17.29,30 Uracil has also been employed.31 Progress with directing groups includes the demonstration of ipso addition to a 1-OMe substituted allyl,32 and di§erentiation of leaving groups in a 2-silyl-1,4-diacetoxybut- 2-ene system.33 A 1-phenyl substituent on the allyl directs x in an unusual phenoxycarbonylation.34 The 1-phenyl substitution pattern also figures in a rearrangement of allylic sulfoximines to a§ord N-tosyl allylic secondary amines.35 A range of other substituents can also give good control.36 Direct cyclisation of pendant tosylamines37 and 4-methoxybenzylamines38 also o§er good routes to cyclic amines.More unusual procedures include switching pathways between nucleophilic centres in 20,39 and between pathways that follow on from the opening of silyl-substituted allylic epoxides (Scheme 3).40 Carbon dioxide has been used to promote substitution of allylic alcohols.41 Displacement of a formate ester from 21 is the first step in a stereocontrolled reduction. This works best with the SO 2 Tol substituent and constitutes a key step in a synthesis of ([)-solavetivone (Scheme 4).42 Chirality transfer from chiral allylic starting materials is a well established route to enantiopure products.An unusual example rearranges a SiPh 2 SiMe 2 Ph ether to form an allylsilane with an SiMe 2 Ph substituent.43 Enantiopure vinylcyclopropanes have been made by chirality relay in a cyclisation process.44 Allylic acetates can be epimerised by palladium catalysts and this has been applied to an enzyme mediated dynamic kinetic resolution process; enzymes and palladium catalysts can be used together.45 In another rearrangement linalyl acetate gave geranyl acetate.46 This is a simple but convenient process. Another simple use of allylic substitution is the removal of allylic protecting groups from nitrogen47 and oxygen.48 200 G.R. Stephenson SO2Tol O H O 21 SO2Tol ( R) H R S 9 1 i Scheme 4 Reagents i Pd(acac)Bun 3 P HCO 2 H Et 3 N TfO OTf OTf R 22 + Ph3Si MgBr 99% ee 53% yield i Scheme 5 Reagents i PdCl 2 [(S)-Alaphos] LiBr Et 2 O–PhMe Palladium catalysed coupling reactions Asymmetric modifications The flow of papers reporting asymmetric coupling has slowed though not due to diminished importance of the topic–the search is on now for highly enantioselective examples.Chemical yield of 98% combined with an ee of 99% sets the standard in an asymmetric Heck coupling using 2,3-dihydrofuran and a chiral P,N-type ligand (the But analogue of 15).49 Enantioselection in the oxidative addition of palladium catalysts to 22 allows symmetry splitting by coupling to magnesium acetylides (Scheme 5).50 Heck coupling chemistry Coupling to allylic alcohols has been controlled to retain the alcohol feature51 as an alternative to the common rearrangement to substituted ketones (e.g.in a recent glycal synthesis).52 A further option is demonstrated with methyl 4-hydroxybut-2-enoate to introduce a lactone substituent.53 Allyl amine derivatives have been used with aryl halides54 and enol triflates.55 Regiocontrol of the destination of the C––C double bond has been addressed by Hallberg’s group in five-56 and six-membered57 rings. More unusual coupling partners include hypervalent iodonium salts,52 diazonium salts,58 diaryltellurium compounds,59 MeF 2 SiCH––CHPh,60 and highly substituted heterocycles such as 23 which promises access to C-nucleoside analogues.61 Gene� t’s group has produced intra-62 and inter-molecular63 examples where regiocontrol of the site of coupling is switched by choices of reagent or conditions.The latter case uses a formic acid trap to e§ect overall reduction. This is becoming a popular procedure and in the case tt forms 24 constitutes an alternative to conjugate addition (Scheme 6).64 Heck coupling has been performed on a solid support65 (a prerequisite for its use in combinatorial library synthesis) at high pressure,66,67 and in molten salt media.68,69 The use of clusters as catalysts has been examined.70,71 NMR analyses72,73 and kinetics74 have been used to study Heck coupling. Applications in synthesis include key steps in routes to carbapenems,75 pyrimidine 201 Organometallic chemistry the transition metals N N Cl I 23 O N N Cl O i 81% N O Ph O I N O Ph O 24 ii Scheme 6 Reagents i Pd(OAc) 2 AsPh 3 Et 3 N Ag 2 CO 3 ; ii Pd(OAc) 2 (PPh 3 ) 2 HCO 2 H Et 3 N nucleosides,60 vincadi§ormine,76 ellipticine,77 cardenolides,78 and in a total synthesis of optically active chanoclavine-I.79 Heck coupling is a mature reaction where the scope is well defined which can be applied with confidence in synthesis and where the thrust of onward development strives for enhanced control.Suzuki chemistry Suzuki coupling to a§ord biaryls tolerates considerable steric constraints as shown in an example which combines pentasubstituted aryl halides and arylboronic acids.80 Another striking application produces rod-like oligo-p-phenylenes from 4-biphenylboronic acid and 1,4-dibromoarenes.81 Stepwise replacement in 1,2-dibromides has been described.82 Examples this year point to heterocyclic coupling partners with substituted pyridines being particularly in vogue.83–86 Examples with indoles,87 pyrrolopyrimidines 88 and pyrroles,89 show the scope of this coupling process.In the last example both triflate and boronic acid components were heterocycles. A variety of boronic esters can be used (from 1,2-90,91 and 1,3-diols92) and other organoboron derivatives.93 As with the Heck reaction use of clusters71 and polymer supports has been examined,94,95 and less usual coupling partners evaluated (iodonium96 and aryldiazonium97 salts) self-coupling of two arylboronates,98 and sp3 carbon centres in this case a cyclopropyl iodide).99 Uses in synthesis include routes to rigidin88 and the left hand subunit of milbemycin b3.100 Stille chemistry Hindered biaryl systems101 and heterocycles have also been targeted in developments of the use of Stille coupling.Heterocyclic tin reagents such as pyrrole,102 furan103 and thiophene104 present no problems. The tin reagent 25 a§ords dimethyl sulfomycinamate 26 (Scheme 7),105 and the thiophene system has been used to make orthogonally- 202 G.R. Stephenson N MeO2C O N O Me OTf N S Bu3Sn CO2Me N O N O Me MeO2C S N CO2Me i 25 26 Scheme 7 Reagents i Pd cat. LiCl fused oligothiophenes,106 or end-capped linear oligomers.107 Coupling of organotin components to heterocycles is also well represented. Selectivity has been observed with dihalopurines,108 and other examples include chiral oxazolines,109 pyrrolidone derivatives,110 thiazolines,111 pyridines,112 and 27113 and 29,114 which a§ord hydrogen bonded oligomers (28) and (30) (Scheme 8) a ligand designed to impose tetrahedral coordination.Copper salts (as used in the preparation of 28) have been evaluated as promoters in coupling with enol triflates.115 Selectivity for iodide replacement in the presence of SO 2 CF 3 ,116 and tin in the place of boron,117 illustrate possibilities for control and unusual variants include coupling to allyl carbonates (a hybrid Stille–allylpalladium chemistry),118 and the introduction of an allyl alcohol substituent with 31 (Scheme 9).119 Syntheses of asuka-mABA and limocrocin,120 a macrolide related to macrolactin A,121 phosphorylated tyrosine derivatives,122 oligonucleotides bearing a tricyclic carbazole,123 and ([)-papuamine and ([)-haliclondiamine124 all rely on important Stille coupling steps. The latter example e§ects homocoupling of alkenylstananes with copper promoted conditions and PdCl 2 (PPh 3 ) 2 in air to close a 13-membered ring.Coupling to anions Organometallic nucleophilic coupling partners extend the use of organotin reagents to other metals currently most commonly zinc. Polymer-supported chemistry has been achieved here too.125 Propyl,126 butyl,127 and more interesting iodoserine-derived alkyl-zinc halides128 have been used. Alkene (e.g. trifluoromethyl-129 and OCONEt 2 - substituted130 alkenylzinc bromides) and arene131–133 examples are more closely related in scope to the Stille counterparts. Again the heterocycle theme continues with indole134,135 and oxazole136 examples and a heteroorganoaluminium coupling reaction. 137 In another case where zinc is superseded hydrozirconation is combined with palladium catalysed coupling to form arylselenobutadienes.138 Zinc cyanide o§ers a change of nucleophile,139 and there has been a flood of applications of palladium catalysed coupling with nucleophiles for the amination of aryl iodides,140–143 including an intramolecular example which forms indolines and tetrahydroquinolines,144 and a similar approach to the synthesis of aminopyridines.145 Possibly the most interesting nucleophile this year is Ph 2 PH which has been used to elaborate aryl triflates in syntheses of phosphine-containing amino acid analogues.146 Coupling to alkynes The combined use of copper and palladium salts is now classic for coupling alkynes 203 Organometallic chemistry the transition metals N N Br Br 27 + NH Me3Sn SnMe3 HN ButO O OBut O N N ButO O OBut O N N H N N NH N ButO O OBut O H n H i N N Cl Cl Me3Sn CN + N N CO2H CO2H 30 29 28 ii iii iv Scheme 8 Reagents i PdCl 2 (PPh 3 ) 2 CuBr; ii Pd(PPh 3 ) 4 ; iii EtOH HCl; iv HCl aq AcOH Me I + Sn O Bu2 31 i Me OH Scheme 9 Reagents i Pd(PPh 3 ) 4 ; LiCl DMF with alkenyl and aryl halides.In the alkenyl series routes to polyenes,147 enynes148 and diynes149 are attractive. This coupling can be performed in the presence of an aryl telluride substituent and an alkenyl halide.150 With arenes aryl bromides151 and 204 G.R. Stephenson N SiMe3 PhSO2 32 N PhSO2 SiMe3 i 95% ee Scheme 10 Reagents i Pd cat. TRAP HOAc iodides152,153 are still typical but as with the other coupling processes described this year there is interest in diaryliodonium salts.153,154 An aryl iodide can be displaced in the presence of an aryl chloride.155 Triflates are convenient coupling partners.156 Examples of coupling with heterocycles remain a major theme with two procedures described for thiophenes using Pd(PPh 3 ) 4 (CuI Et 3 N;157 CuBr LiBr piperidine158) one with pyrroles,159 and one with 2-chloroquinolines.160 These alkyne couplings are sometimes mixed with aspects of the procedures described above as in coupling between alkynylzinc reagents and 3-iodopropenoic acid (without protection),161 and procedures that use alkynyltin reagents.162,163 Tributyltin hydride is an additive in a one-pot procedure to prepare enediynes,164 and a distannylalkyne is linked at both ends to iodobinaphthyls in a synthesis of a bisbinaphthol.165 Substituted uracils,166,167 nucleosides,168 terinafine,169 (])-himbacine170 and the neocarzinostatin chromophore171 show the power of the reaction in recent synthetic applications and two examples the construction of rod-like conjugated polyynes172 and dendrimers with dialkynylarene links,173 illustrate the use of alkyne coupling in materials science.Combining alkenes and alkynes Asymmetric modification of alkene-to-alkyne coupling has been reported.174 The procedure works excellently with 32 (Scheme 10). The usual products from alkene-toalkyne coupling are 1,3-dienes. Switching to form alkenyl chlorides can be e§ected with LiCl–CuCl 2 additives.175,176 Cycloaddition gives access to combinatorial libraries by a route with alkene-toalkyne coupling as the first step.177 The reaction is a key step in Trost’s synthesis of (])-cassiol,178 Kibayashi’s synthesis of (])-streptazolin,179 and Fukumoto’s formal total synthesis of (])-aphidicolin,180 and a reductive version (using polymethylhydrosiloxane and acetic acid) was used by the same research group for (])-pumiliotoxin C.181 Coupling two alkynes is a key step on the way to siccanin.182 Tandem and cascade coupling reactions Asymmetric palladium catalysis The asymmetric Heck procedure described earlier can be combined with an additional C–C bond formation by the anion capture process.This tandem reaction gives 87% ee and has been applied in a total synthesis of ([)-*9(12)-capnellene.183A more extensive asymmetric tandem process figures in a synthesis of (])-xestoquinone. The cyclisation of 33 gave the product in 67% ee (Scheme 11) leaving only hydrogenation of the alkene and conversion into a quinone to complete the synthesis.184 Palladium catalysis in tandem coupling Oxidative addition followed by a sequence of bond formations to alkenes is a typical 205 Organometallic chemistry the transition metals OMe OMe O O O Tf 33 MeO MeO O Me O i Scheme 11 Reagents i Pd 2 (dba) 3 (S)-(])-BINAP PMP O I i O NR2 34 Scheme 12 Reagents i Pd(OAc) 2 PPh 3 K 2 CO 3 H 2 C–– C––CH 2 NHR 2 tandem process.With 33 the final step is b-elimination but if the last alkene carries an organotin substituent insertion into the C–Sn bond and reductive elimination can finish the cycle.185 Anion capture can also end the sequence.186 An allylic acetate can serve either at the end187 or at the start.188 Tandem cyclisation has been performed with allyloxy substituents and the C––C link of a dehydro-sugar.189 Aryl iodides are good for the initial oxidative addition and cyclisations employing alkenes and b- elimination,190 an organotin ending,191 or an intermolecular combination employing cyclisation via a p-allyl intermediate,192 have been described.An alkyne can pick up the intermediate formed by oxidative addition. Alkenes also end the process,193 but anion capture by formate194 or intramolecular addition of a carboxylate group195,196 provide alternatives. Coupling a prop-2-ynyl ether-substituted aryl iodide with allene and an amine brings four components together in sequence to form 34 (Scheme 12).197 The alkene–alkyne coupling process can be combined with C–C bond formation with an aryl halide,198 or anion trapping with NaBPh 4 .199 Other variations combine alkenyl triflate with allene and an enolate,200 or e§ectively add CN and an acyl group across an alkyne.201 Iodophenols add across alkynes to form benzofurans.202,203 Intramolecular cyclisation of an aryl iodide with two alkynes forms a central aromatic ring,204 and an alkene with two alkynes forms a cyclohexadiene.205 Enynes cyclise to form 1,4-disubstituted arenes,206 and two molecules of ethyne combine with tin reagents to form stannoles.207 Examples of cyclopropane ring-opening reactions during tandem processes lead to a wide variety of structures.208–213 The current emphasis in research on modification of reactions to allow them to be performed on a polymer support has borne fruit in the field of tandem coupling.214 An example of a three component coupling using a dihydropyran-functionalised polystyrene has been described.215 Tandem reactions combined with carbonylation have been popular adding an alkenyl halide and CO across an alkyne216 or alkene.217,218 Closure of a phenol to an 206 G.R.Stephenson N2 O O O H H Me O 38 N O O H SO2Ar Rh Rh 4 i Scheme 13 Reagents i RhII catalyst Ar\4-(C 12 H 25 )C 6 H 4 room temperature alkene,219 or intermolecular combination of bromoaniline and alkenyl halide derivatives with carbonylation a§ords lactone219 and lactam220 products respectively. A triple carbonyl insertion has been described.221 Wacker oxidation and 1,4 difunctionalisation When modified for intramolecular nucleophile addition the Wacker oxidation can form skeletal bonds. Cyclic hemiacetals are the product.222 This cyclisation has been performed on a carbohydrate framework.223A lactone forms when a trimethylsilylalkyne is used in place of the normal alkene.224 1,4-Difunctionalisations is a related process and e§ective cyclisation reactions can be achieved.Interception of the palladium allyl intermediate with a chloride from LiCl is a common strategy,225 but with correctly placed branching on the diene b-elimination can be brought into play to leave a diene in the product.226 The mechanisms of both the 1,4-difunctionalisation,227 and Wacker228 reactions have been under investigation during 1996. Catalysis of carbene additions and insertions Asymmetric rhodium catalysis Just as palladium dominates coupling chemistry so rhodium dominates carbene addition and insertion. Asymmetric modification of this chemistry is receiving great attention.Cyclic amides such as 35229 and 36230 have proved useful ligands in cyclopropanation but optical yields are variable. Proline-derived ligands such as 37 have been popular,231–233 and since any chiral carboxylic acid can be used wide selections of chiral ligands can be surveyed.234,235 Asymmetric cyclopropanation has been combined with a Cope rearrangement to access the tremulane skeleton in 38 using a long-chain variant of 37 (Scheme 13).236 Optical purity of the product however was poor. Chiral auxiliaries attached to the diazo ligand have also been employed.237,238 N O O OMe 35 N O 36 PhthN N H O O 37 4-BuC6H4SO2 207 Organometallic chemistry the transition metals Rhodium catalysed insertion The conceptually most straightforward use of rhodium carbenes is in CH insertions.A diazo ester can be cyclised onto an otherwise unactivated CH 2 group forming a new bond where normally this would not be possible.239 Insertion next to silyl ethers,240 at allylic positions241 and at the CH 2 of allyl ether substituents242 are among the examples described this year. Sometimes the outcome is elimination and this gave a simple synthesis of (Z)-a,b- unsaturated carbonyl compounds.243 Reaction with amine N–H bonds makes amino acid derivatives. PhC–– N 2 CO 2 R244 and CF 3 C––N 2 CO 2 R245 a§ord phenyl- and tri- fluoromethyl-substituted products. MeCOC––N 2 CO 2 Me has been used with Z-protected alinamide at the start of a synthesis of (])-nostocyclamide.246 Insertion into a Si–H bonds has been described.247 With aromatic rings simple cyclisation of a substituent by C–H insertion is sometimes the major reaction pathway.248 Rhodium catalysed cyclopropanation Cyclopropanation is also a straightforward outcome and has been reported in both inter-249 and intra-molecular250 versions.Such reactions are finely balanced and other cyclisation products can dominate.251 When ‘cyclopropanation’ occurs at an aromatic ring ring expansion a§ords a substituted cycloheptatriene.252 A rhodium catalysed aziridination has been described.253 Rhodium catalysed addition Rhodium carbenes are electrophilic and this can initiate more elaborate chemistry through addition at C––C bonds in dihydrofuran (in a formal total synthesis of aflatoxin B 2 )254 and pyrroles.255 Reaction at the oxygen of cyclic ethers (resulting in ring expansion)256 or ketones257,258 e§ects cyclisation and intermediates can be trapped in further conventional cycloaddition reactions.258,259 Other metals Palladium catalysts have been used to e§ect cyclopropanation with diazo esters,260 and nickel(0) carbene intermediates have been proposed in reactions that form alkenes from gem-dihalides.261 Cu(acac) 2 is popular in the place of Rh 2 (OAc) 4 ; examples continue to appear.262 Alkene metathesis Molybdenum and ruthenium catalysts are currently most popular and asymmetric modification of the molybdenum alkylidene system with the complex 39 provides an example of kinetic resolution in ring-forming catalysis.263 This type of cyclisation in which a ring is formed by loss ofH 2 C––CH 2 from a pair of terminal alkenes is proving very popular with synthetic chemists.Simple examples that form nitrogen heterocycles illustrate the two now classic catalyst systems 40264 and 41.265 Dihydrothiophene has been made by cyclisation of diallyl sulfide which was possible with the molybdenum catalyst but not with 41.266 Cyclisation on a carbohydrate framework appears in a formal total synthesis of castanospermine.267 Applications to form larger rings are particularly attractive with products 42,268 43,269 44,270 and linked amino acids271 resulting from ruthenium268–270 and molybdenum271 catalysis.The lack of stereodefinition in 43 was not a problem since the 208 G.R. Stephenson O O O O O O H H O O H H 45 46 i ii Scheme 14 Reagents i 3mol% 41; ii 13mol% 40 H O F3 C CF3 Mo Ph N H O F3C CF3 39 O F3C CF3 Mo Ph N Me O CF3 40 CF3 PCy3 Ru PCy3 R Cl Cl 41 N O H O 42 O O MeO MeO 43 O O 44 R = Ph or CH CPh2 alkene was merely a consequence of the cyclisation strategy and was reduced out to complete (])-lasiodiplodin.The ruthenium system has been used with allylglycines in peptides either in solution or on solid supports.271 Similar applications appear in syntheses of the carbocyclic nucleoside 1592U89272 and novel b-lactams.273 There have been some nice applications in polyether synthesis; ruthenium was used for synthesis of 45,274 and molybdenum for 46 (Scheme 14).275 Dibenzocrown ethers with a –OCH 2 CH––CHCH 2 O– link,276 and dimers of cyclodextrins with –OCH 2 CH 2 CH––CHCH 2 CH 2 O– spacers277 have been made using 41 (R\CHPh). TheCH–CH––CPh 2 version of the catalyst has been used to modify ferrocene substituents278 and to form liquid crystal oligomers.279 The combination of 47 with hex-3-ene forms a tetrasubstituted cyclopentane.280 A polymer-supported metathesis process has been described.281 Enyne metathesis by ruthenium282 or molybdenum283 can a§ord varied products such as 48282 or 49.283 In the case of 50 a tandem cyclisation has been achieved (Scheme 15).284 Diynes have also been cyclised by metathesis reactions using a polymer-mounted molybdenum system.285 209 Organometallic chemistry the transition metals CO2Me CO2Me N O Me 47 48 O2N O N O 49 OSiEt3 Me OSiEt3 i 50 Scheme 15 Reagents i 41 R\CHCHCPh 2 As far as the development of organometallic catalysts is concerned the exploration of the scope of these two complementary metathesis catalysts 40 and 41 has been the great success story of 1996 reminiscent of the great push to begin the serious exploitation of palladium catalysed coupling a few years ago.2 Synthetic chemistry by stoichiometric procedures g1-Complexes Organotitanium and zirconium chemistry The stoichiometric chemistry of r-bonded complexes of titanium and zirconium provides a highly fully developed system for synthetic transformations. The chemistry resembles a catalytic cycle in slow motion with the advantage that reaction conditions can be varied along the pathway and reactants can be added at intermediate stages. Initial introduction of the zirconium often proceeds with concomitant C–C bond formation as in an elegant application towards the dolabellane skeleton. Linking two double bonds at the first step provides an intermediate bis-g1 complex. Now an organolithium nucleophile (CH 2 ––CMeCHClLi) is added and the resulting zirconate rearranges with displacement of Cl to a§ord an g1,g3-allyl intermediate which is trapped by electrophiles.286 The zirconacycle formed by linking two alkynes can combine with 1,2-diiodobenzene to form substituted naphthalenes.One C–C bond is formed in the reaction that introduces the metal and a further two are made as the metal is detached.287 Titanium and zirconium cyclise enynes to a§ord g1,g1 metallacycles which are decomplexed with acid.288 The product of hydrozirconation of an alkyne has been used as a nucleophile with an epoxide in a synthesis of (])-curacin A.289 Cyclopentadienylirondicarbonyl chemistry In the classic g1-CpFe(CO) 2 series carbonyl insertion promoted by Lewis acids has 210 G.R. Stephenson Me O (CO)3Cr Me (CO)3Cr (CO)3Cr Me OH CO2Me Mn(CO)4 O i ii 51 Scheme 16 Reagents i PhCH 2 Mn(CO) 5 ; ii CH 2 ––CH 2 CO 2 Me Cl N NMe2 + Me Mo(CO)3 N NMe2 Mo(CO)3 Cl N Mo(CO)3Cl Ph Ph NMe2 i ii 52 Scheme 17 Reagents i room temp.; ii Ph-C–– – C-Ph been explored.290 A naphthalenylmethyl complex has been prepared from bromomethylnaphthalene and compared with the corresponding Co(CO) 4g1-complex.291 Related CpW(CO) 3 complexes have been prepared from 7-bomohept-6-ynal by bromide displacement and cyclisation.292 CpFe(CO) 2 bound to the nitrogen of maleimide has been used to elaborate amino acids.293 Cyclopentadienylironcarbonyl triphenylphosphine complexes are now famous as chiral auxiliaries. Asymmetric elaborations of the acyl groups –COCH 2 Ph294 and –COCH 2 SMe,295 have been examined.Tetracarbonylmanganese chemistry ortho-Metallated aryl ketone complexes react with PhNSO to form an imine with loss of SO 2 .296 Under di§erent conditions however SO 2 inserts into the C–Mn bond.297 The cyclometallation can be performed in the presence of a tricarbonylchromium group (vide infra) on the aromatic ring and the reactivity of the C–Mnbond leads to 51 as the major product (Scheme 16).298 In a reverse approach to the related cyclometallated molybdenum complex an g6-arene donates the metal by oxidative addition to form 52 which can be elaborated by reaction with alkynes (Scheme 17).299 g2-Complexes Cyclopentadienylrheniumnitrosyl chemistry Complexation of unsaturated alcohols by CpRe(NO)PPh 3 a§ords cationic g2-complexes. Chemoselective oxidation and Wittig extension a§ord 53 which can be reduced at the ketone in the presence of the rhenium (Scheme 18).300 Hydride reduction of a four-electron rhenium alkyne complex gives 54.301 g3-Complexes Tetracarbonyliron chemistry Diastereoselective complexation of an enantiopure allylic benzoate gives the precursor for the cationic chiral g3-complex 55 which reacts with nucleophiles with complete 211 Organometallic chemistry the transition metals Cp Re ON PPh3 Me O Cp Re ON PPh3 HO Me + + Re H Ph Ph Cp Br i 53 54 Scheme 18 Reagents i NaBH 4 MeOH O O Me CpW(CO)2 59 O O HO H Me 65% i ii iii Scheme 19 Reagents i NO`; ii I~; iii (CH 3 ) 2 CHCHO stereocontrol to set a new chiral centre in the metal-free product.302 The SO 2 Ph group directs nucleophiles to the far end of the p-system.The ester in 56 has the same e§ect and this electrophile has been used with an enantiopure enamine nucleophile in a kinetic resolution that gives a product in 64% ee.303 Enantiomerically enriched 57 has been used stereoselectively with prochiral nucleophiles.304 The related neutral Fe(CO) 2 NO complex 58 and an ester analogue have been resolved and their CD curves reported.305 Me SO2Ph Fe(CO)4 BF4 – + CO2Me Fe(CO)4 BF4 – + Me CO2Me Fe(CO)4 BF4 – + Me Fe(CO)3NO 55 56 57 58 NHR* O Cyclopentadienyltungstendicarbonyl chemistry Development of the cyclopentadienyltungsten complexes continues in the Liu group.g1-Prop-2-ynyl structures rearrange to give complexes such as 59 which can be converted into cationicCpW(CO)NO complexes which react with iodide and can then be elaborated as nucleophiles (Scheme 19).306 g3-CpW(CO) 2 complexes have been formed by alkylidene migration.307 g4- and g5-Complexes Tricarbonyliron chemistry The continued development of routes to carbazole natural products nicely illustrates how e§ectively the chemistry of the g5-cyclohexadienyl complexes and the g4-cyclohexadiene counterparts can be exploited together.Nucleophilic attack by the specifically substituted aminobenzofuran 60 is followed by oxidative cyclisation with I 2 to complete the first total synthesis of furostifoline (Scheme 20).308 The use of the now 212 G.R. Stephenson Fe(CO)3 + BF4 – + Me NH2 O Fe(CO)3 Me NH2 O NH O Me 60 i ii OMe NH2 Fe(CO)3 D 61 Me Me (OC)3Fe NH OMe Me Me H H ii Scheme 20 Reagents i MeCN; ii I 2 py OMe O MeO Fe(CO)3 62 HN OMe Fe(CO)3 + O 63 HN OMe Fe(CO)3 64 i ii iii O Scheme 21 Reagents i,Me 3 SiCN; ii H 2 NNH 2 ; iii H 2 Raney Ni more familiar oxidising conditions (MnO 2 or Cp 2 FePF 6 ) failed in this case but are normally309 widely applicable and convenient for the formation of dihydrocarbazoles.With two-electron oxidising agents good regio- and stereo-selectivity has been observed for the removal of the 6-syn hydrogen (or the corresponding deuterium in 61) but regioselectivity depends on the nature of the oxidising agent.310 Addition of CN to a cyclohexadienyl unit followed by reduction puts in place a –CH 2 NH– fragment. In the case of 62 reduction and cyclisation take place in the same reaction to form 63 (Scheme 21).311 The regioisomeric amide 64 was prepared by cyclisation of an aminoalkyl side-chain to the nitrile. The trimethylsilylalkyl ester 65 introduces a precursor to a –CH 2 CH 2 NH– fragment.This approach is used to form 66 (Scheme 22) in a formal total synthesis of lycoramine in which the presence of donor substituents on the arene flattens the structure of the cyclohexadienyl complexes to allow the nucleophile in to build the quaternary centre.312 Amines have been added directly to cyclohexadienyl complexes.313 This has been employed with an optically active exocyclic dienyl complex.314 Novel organometallic ligands have been made in this way using Ph 2 PH in place of the amine.315 Addition of an amino acid derivative provides 213 Organometallic chemistry the transition metals MeO MOMO OMe Fe(CO)3 + BF4 – MOMO OMe NC O SiMe3 O MeO MeO CN ii iii iv v NC O SiMe3 O 65 66 O O Fe(CO)3 i Scheme 22 Reagents i NaH; ii TBAF; iii Me 3 NO; iv (CO 2 H) 2 then 10%H 2 SO 4 ; v aq NaOH diastereomerically pure N-protected amino acids under the control of the chirality of the metal complex.316 The chemistry of 1-methoxy- and 1-acetoxy-cyclohexadienyl complexes and their acyclic counterparts 67 and 68 has been described.317 The corresponding pair of substituents SPh318 and SO 2 Ph319 have also been examined.With an alkene extension conjugate addition of nucleophiles is possible. In the case of 69 a prochiral centre MeO Fe(CO)3 PF6 – AcO Fe(CO)3 PF6 – Fe(CO)2PPh3 Me + PF6 – 67 68 69 + + is present and reaction with Ph 2 CuLi gives an 8:1 mixture of diastereomers.320 This cyclohexadienyl complex was itself obtained by nucleophile addition to 70 and replacement of CO by PPh 3 in a later step.The Fe(CO) 2 (Ph 3 P) complex 71 has been prepared by CO–phosphine exchange.321 Structures 67–73 illustrate the increasing range of substitution patterns now available. Donor alkoxy substituents at C-1 in 67 70 and 71 and the PhS in 72 (with hard nucleophiles) draw nucleophiles to the site of substitution. This same e§ect has been used in the cycloheptadienyl series with eucarvone-derived Fe(CO) 2 (PhO) 3 P complexes.322 Intermediate acyclic pentadienyl structures are responsible for a new organoiron mediated route to trans-1,3-disubstituted 1,4-dioxanes,323 and dienylic fluorides.324 With acyclic dienyl complexes cisoid or transoid intermediates are possible and with the fluoride addition procedure good results were obtained by in situ replacement of a leaving group by fluoride while the corresponding reaction of an isolated dienyl salt failed.214 G.R. Stephenson MeO OMe Fe(CO)2L L = CO 70 L = PPh3 71 Fe(CO)3 + + PhS Fe(CO)3 + PhS O O 72 73 Neutral diene complexes can themselves impart important stereocontrol as in aldol chemistry at an aldehyde adjacent to the g4-complex. Reduction of the ketone in the product a§ords a 1,3-diol unit needed for a C-7–C-20 fragment of macrolactin A.325 Homoallylic alcohols have been used as a starting point to address this structural feature in a C-11–C-24 fragment.326 Access to substituted piperidines completes tricarbonyliron mediated syntheses of dienomycin C and its C-4 epimer.327 Dihydroxylation 328 cycloaddition329,330 and radical addition330 have also been examined. Functionalisation of imines next to the g4-Fe(CO) 3 unit has been used in the synthesis of a dipeptide isostere.331 Friedel–Crafts acylations form cyclic ketones in which a portion of the metal-bound diene lies within the ring.332 E§ects arising from the presence of Fe(CO) 3 can be subtle; an example of enhanced macrolactonisation has been described.333 Neutral cyclohexadiene g4-complexes have also received attention in studies of 1,3-diacetoxy substitution patterns334 and with furanyl substituents.335 The latter give convenient access to 1,4-dicarbonyl-2-ene functionality by ring opening.Dipolar cycloaddition at an exocyclic alkene,336 oxidation of alkenyl side-chains,337 and palladium catalysed replacement of OTf at C-1 of the g4-unit338 have been described. A rhodium catalysed diazo ester insertion (vide supra) has been reported adjacent to the g4-complex.339 The precursor was obtained by a dianion addition an example of the successful use of an unusually basic nucleophile.4-Bromotropylium complexes of Fe(CO) 3 interconvert.340 Moving to small rings intramolecular trapping of cyclobutadiene liberated from its Fe(CO) 3 complex forms polycyclic structures.341 There is also an important g3 chemistry of Fe(CO) 3 complexes and progress has been particularly marked in the ferralactone series available by iron mediated opening of alkenyl epoxides. Aldehydes342 and ketones343 besides the allyl complex react diastereoselectively with nucleophiles. The ferralactone carbonyl group can also be exploited and has been converted into the alkoxycarbene 74.344 Me O (CO)3Fe OMe + 74 Special notice should be taken of the strategically important reactions that remove the metal with C–C bond formation.Intramolecular procedures currently show most promise. Deprotonation of the ester 75 brings about macrocyclisation when performed at room temperature but the protonation step lacks regiocontrol a§ording a 3:4 mixture of 76 and 77 (Scheme 23).345 Deprotonation followed by oxidation e§ects 215 Organometallic chemistry the transition metals O O H (CO)3Fe 75 O O 76 O O 77 + CO2Et (CO)3Fe HO2C CO2Et 78 58% i ii i iii Scheme 23 Reagents i LDA CO; ii H`; iii O 2 carbonyl insertion as illustrated in the cyclisation that makes 78. Similar nitrile mediated cyclisations start with addition of a Cu–Zn reagent to a pentadienyliron complex followed by cyclisation upon decomplexation.346 A similar start exploits a cycloheptadienyl complex to end with the introduction of a formyl substituent by carbonyl insertion and protonation of the anionic acyl intermediate.347 Nucleophiles can also add to cycloheptadienyl complexes for form g3,g1-products with a r-bond to the metal which can directly undergo carbonyl insertion.A sequence of two cycloheptadienyliron mediated bond-formations has been performed before carbonylative decomplexation makes 79 a regioisomer which results from double bond migration (Scheme 24).348 The g3,g1-intermediates can also be accessed by opening alkenylcyclopropanes. 349 Insertion of CO in this system can be promoted with ceric ammonium nitrate.350 Investigations into the formation of non-racemic tricarbonyliron complexes have focussed particularly on improved methods of asymmetric induction during the complexation of prochiral diene ligands.Terpene-derived a,b-unsaturated imines351 and binaphthyl-based systems352 have been described. In the latter case asymmetric catalysis has been achieved. Covalently attached auxiliaries can also induce chirality during complexation and the use of esters and amides,353 and sulfinyl groups,354 have been described. Tricarbonyliron complexes have been separated by HPLC on cyclodextrin-based columns.355 Trimethylenemethane complexes have been resolved by temporary covalent attachment of lactate esters.356 Resolution using ephedrine adducts of aldehydes has provided labelled enantiopure substrates to examine the selectivity of yeast reduction of functionality in the presence of the Fe(CO) 3 group.357 The desymmetrisation of meso structures is possibly the neatest of the methods that use preformed g4-complexes.Alkyl group transfer from a dialkylzinc reagent in the presence of an amino alcohol auxiliary gives 80 in high ee (Scheme 25).358 The absolute configurations and CD curves of methyl-substituted butadiene complexes have been examined.359 A crystal structure of the symmetrical 2,4-dimethylpentadienyl complex has been described,360 and the electrochemistry of cyclohexadienyliron complexes has been examined.361 Mechanistic details in the chemistry of heterodiene tricarbonyliron complexes have 216 G.R. Stephenson But Fe(CO)2P(OPh)3 + But Fe(CO)2P(OPh)3 Ph O But Ph 79 i ii Scheme 24 Reagents i PhLi; ii CO O O Fe(CO)3 O Et Fe(CO)3 N OH Ph Ph Me i 53% 98% yield ee > 80 OH Scheme 25 Reagents i Et 2 Zn Me3Si Li Me3Si • O OEt Fe(CO)3 81 i ii Scheme 26 Reagents i Fe(CO) 5 ; ii EtOS(O) 2 CF 3 been elucidated.Vinyl ketone complexes are converted into vinylketene complexes with retention of configuration ruling out the possibility of symmetrical carbene complexes as intermediates.362 Vinylketene complexes form vinylketenimines by heating with isonitriles. Again there is retention of configuration.363 Photochemical isomerisation during complexation brings alkenes into conjugation with esters to form g4-2-alkoxyoxadiene structures.364 Vinylimine complexes with C-2 methyl substituents are converted into 2-aminodiene complexes by a rearrangement initiated by deprotonation with PhNHLi.365 Fluxionality in vinylimine complexes has been studied,366 as has the activation energy for bond-shift isomerism in g4-complexes of OCH–CH––CH–CDO.367 Vinylketene structures have been synthesised by a double carbonyl insertion in yields as high as 55%.Like decomplexation with concomitant C–C bond formation (discussed above) reactions that form g4-tricarbonyliron complexes during the process that fashions the p-bound ligand are also strategically important. The formation of 81 (Scheme 26) and the PPh 3 analogue has provided a nice example.368 When cationic g4-complexes are required CpMo(CO) 2 is a popular choice. Kno� lker has extended his organoiron routes to carbazoles to employ this Mo system in total syntheses of mukonal369 and murrayacine.370 Lactone and bicyclic amine products can also be obtained from the metal removal step.371 Organocopper–zinc nucleophiles with g4-electrophiles provide a convenient entry.The regiodirecting e§ect of a C-2 PhS group has been defined as x (i.e. nucleophiles add at C-4).372 A related molybdenum structure bound to cyclopentadienone has been employed with nucleophiles. 373 A (C 5 Me 5 )Mo(CO) 2 g3-c-lactonyl complex has been investigated in 217 Organometallic chemistry the transition metals N O NC Cr(CO)3 N O H NC i ii 82 Scheme 27 Reagents i LDA; ii I 2 reactions with nucleophiles and protons,374 and sugar-derived allylic acetates have been converted into TpMo(CO) 2 complexes by oxidative addition [Tp\hydridotris( 1-pyrazolyl)borate].375 g6-complexes Tricarbonylchromium chemistry Intramolecular nucleophilic additions to complexed arenes have been shown to be reversible but the cyclised product 82 can be trapped by aromatisation of the g5-anion upon oxidation with iodine (Scheme 27).376 Oxazoline substituents promote meta nucleophile addition which can be followed by alkylation of the anion.377 Prochiral imine and oxazoline systems have been used with asymmetrically modified organolithium reagents.378 Leaving groups can be displaced from Cr(CO) 3 -activated arenes to form biaryl379 and arylalkyne380 complexes.Methyl381 and isopinocamphenyl or fenchyl382 auxiliaries attached as aryl ethers have induced asymmetry in the addition of LiMe 2 CCN. The complex of boron heterocycle 83 reacts with acetylides at boron displacing PMe 3 .383 A cationic analogue 84 of benzene(tricarbonyl)chromium has been prepared. 384 B Cr(CO)3 PMe3 83 Cr(CO)2NO 84 + The chemistry of benzylic cation complexes has been taken up by Corey’s group to gain stereocontrol in the synthesis of cetirizine a second generation histamine antagonist.385 Benzoxanthiane386 and benzyl fluoride387 compounds have been synthesized. Benzyl anion complexes feature in the elaboration or aryl acetals,388 and fluorenes.389 When two methyl groups are placed 2,3 to a tert-butyl ester the C-2 group has been shown to be more readily deprotonated.390 Benzylic deprotonation has been used to a§ord desymmetrisation of 85 (Scheme 28).391 Chirality next to the g6-complex is induced by asymmetric deprotonation of benzyl ether complexes392 and secondary ether structures.393 Acetals can be used in the place of ethers.394 Enzymic methods395 and palladium catalysed asymmetric alkoxycarbonylation396 have been employed.Organometal catalysed processes at functionality attached to the g6-unit are interesting in their own right. Other examples include Suzuki coupling with boromoarene 218 G.R. Stephenson O (CO)3Cr O (CO)3Cr SiMe3 Ph N Li Ph 82% 76% yield ee 85 Scheme 28 Cl (CO)3Cr NHBoc CO2Me Zn NHBoc CO2Me I i ii 86 Scheme 29 Reagents i Pd 2 (dba) 3 (o-Tol) 3 P; ii hm Cr(CO)3 Me N Br Cr(CO)3 Me N Br O H (+)-87 Me N O H H (–)-88 OMe OTMS ii iii i Scheme 30 Reagents i SnCl 4 ; ii Bu 3 SnH AIBN; iii air hm complexes to form complexed biaryls,397 and incorporation of the iodoserine-derived organozinc reagent 86 in the synthesis of substituted aromatic amino acids (Scheme 29).398 The chromium influences conventional reactions at adjacent positions in the formation of unsymmetrical acetals,399 1,2-diols,400 (which has been applied to ([)- goniofupyrone401) and amines from imines by reduction402 and addition of Reformatsky reagents.403 Cycloadditions at imines404,405 can be stereocontrolled and in the case of 87 the product has been taken on in a stereoselective radical cyclisation to a§ord the ([)-isomer of 88 (Scheme 30).405 Cyclopropanation,406 elaboration of enones by Grignard reagents (followed by a stereocontrolled oxy-Cope rearrangement) or directly by Lewis acid mediated addition of allylsilanes,407 radical cyclisations of groups introduced through the exploitation of benzyl anions,408 and double functionalisations of (1,2-dioxobenzocyclobutene)Cr(CO) 3 have all been exam- 219 Organometallic chemistry the transition metals ined.409,410 The resulting bis-alkoxides also rearrange by an oxy-Cope mechanism when alkenyllithium reagents are used.Ring opening to form a quinodimethane complex and trapping by cycloaddition,411 and photochemical intramolecular cycloaddition to cycloheptatriene412 and tropone413 complexes make polycyclic products. Intermolecular addition of dienes to cycloheptatriene414,415 and g6-thiepine 1,1-dioxide415,416 complexes are performed under conditions that detach the metal during skeletal bond formation.416 Cycloaddition with alkyl isocyanates also removes the metal,417 and with alkynes a sequence of two cycloadditions and four C–C bond formations occurs during detachment of the chromium.418 A further variant uses an g5-chromium–tin adduct (arising from anion trapping) as the precursor for cycloaddition.419 Besides the specialist ‘expert’ tricarbonylchromium research teams the adoption of this chemistry this year by widely acclaimed general synthesis groups of the stature of those led by Corey385 and Paquette410 is itself a testament to the growing importance of the methodology.Tricarbonylmanganese chemistry Nucleophile addition to the cationic (and hence powerfully electrophilic) tricarbonylmanganese complexes remains the main focus of attention with cine and tele processes described for hydride addition.420 For C–C bond formation LiCH(CN)SiMe 3 can pick up two arene complexes. In the 1,2,3-trimethoxybenzene case described each addition occurs at C-4.421 Mn(CO) 2 phosphine and phosphite systems have been used with LiC(Me) 2 CN.422 With a thiophene Mn(CO) 3 complex nucleophile addition (from organocuprates) occurs at sulfur.423 (Benzothiophene)Mn(CO) 3 ` carries Mnon the arene ring and in a strange reaction an additional manganese complex has been inserted into the arene–sulfur bond.424 An g6-hydroquinone complex has been prepared.425 Reduction dimerises arene manganese complexes.426 Neutral g5-manganese complexes can themselves be elaborated by nucleophile addition,427 for cycloaddition with alkynes.428 Cyclopentadienyliron and ruthenium chemistry Cationic CpRu arene complexes play a key role in Pearson’s route to OF4949 III forming the diaryl ether 89 (Scheme 31) which was then cyclised in a formal total synthesis of the cyclic peptide target.429 Two halides can be displaced from dichloroarenes. 430 Combining 1,2-dichloro and 1,2-dihydroxy substitution patterns affords benzodioxin derivatives,431 and a range of related heterocycles.432 The CpFe system was useto make functionalised p-phenylenediamine compounds by replacement of Cl from 1,4-dichlorobenzene complexes.433 A kinetic study of chlorine replacement has been reported.434 Dicobalthexacarbonyl Nicholas chemistry The focus of attention in recent years on the chemistry of enediyne natural products has provided an important platform for the development of applications of cobalt alkyne chemistry in particular the use of carbocations a to the cobalt-bound alkyne a process now widely referred to as the Nicholas reaction.The diastereoselective conversion of 90 into 91 (Scheme 32) provides a fine example and is drawn from a substantial full paper setting out recent progress in the research of the Magnus group.435 Kinetic 220 G.R.Stephenson MeO OH CO2 Br ZNH Cl CO2Me NH O BocHN NH2 O RuCp PF6 – + OMe HNZ CO2H O NH CO2Me O HN O NH2 89 + i–iv Boc Scheme 31 Reagents i NaO(But) 2 C 6 H 4 ; ii hm CH 3 CN; iii NaI; iv SmI 2 TBSO O OBBu2 O Co Co(CO)3 90 TBSO OH OBBu2 O 91 H 82% i ii OTBDPS (CO)3Co Co(CO)3 H O CO2Me OTBDPS (CO)3Co Co(CO)3 CO2Me H OH 92 91% iii OTIPS O Me TBSO PhS (CO)3Co Co(CO)3 93 OMOM OMOM TBSO Me SPh CO2TIPS 94 60% iv v (CO)3 Scheme 32 Reagents i Bun 2 BOTf Et 3 N; ii cyclohexa-1,4-diene; iii (MeO)MeAlCl; iv 23 °C 24 h; v NMNO 221 Organometallic chemistry the transition metals Me3Si Co(CO)3 (CO)3Co OAc OH O Me3Si Me O O i ii 95 Scheme 33 Reagents i BF 3 ·OEt; ii CAN H H O O (CO)3Co Co (CO)3 O O H H i ii iii O H H 96 Scheme 34 Reagents i C 2 H 4 9 equiv.TMANO·2H 2 O 40 °C 25–30 atm PhMe–MeOH 81%; ii PPh 3 CBr 4 ; iii steps control gives a mixture of diastereoisomers but these equilibrate so 91 can be isolated in 82% yield. Cobalt alkyne chemistry is used the opposite way round to prepare 92 (94% erythro) which was taken on by conventional chemistry to form an enediyne which spontaneously cyclised.436 Temporary attachment of Co 2 (CO) 6 has been used as a protection strategy for enediynes.437 Bending of alkynes by complexation helps the cyclisation that forms 91 and has also been used to influence the transition state geometry in the Ireland–Claisen rearrangement of 93. The preparation of 91 and 94 illustrates the excellent ways438 now available to remove the cobalt when its role in the synthesis is over. The course of deallylcarboxylation has been adjusted by complexation of an alkyne to suit the needs of a synthesis of a carbacyclin derivative which also employs rhodium catalysed diazoester insertion (see Section 1).439 The 1,2-shift of alkynyl groups has been facilitated by complexation.440 Cycloaddition of nitrile oxides to alkenes next to the complexed alkyne is controlled by the stabilisation of charge by the cobalt and so gives excellent regioselectivity.441 Studies of enol ethers in aldol chemistry continue 442 and a case has been developed where a chiral auxiliary associates with the aldehyde.443 With simple leaving group displacement (the original Nicholas reaction) the process has been extended to include the use of alkenes as the nucleophile.This generates a carbocation which will deprotonate to form enyne products or can be intercepted as in the tandem process that forms 95 (Scheme 33).444 Pauson–Khand reaction The formation of monosubstituted cyclopentenones by means of the Pauson–Khand reaction requires the use of ethene.A much improved autoclave procedure employing nine equivalents of trimethylamine N-oxide at an optimum temperature of 40 °C has been developed and demonstrated in a synthesis of (])-taylorione 96 (Scheme 34).445 In a synthesis of (])-b-cupareneone a temporary tether was used in the cyclisation of 97 (Scheme 35).446 An 8 1 ratio of diastereoisomers was obtained. Slightly better (12 1) diastereoselectivity can be obtained at the expense of yield by omitting the 222 G.R. Stephenson Ph O S Ph S O H O i 97 Scheme 35 Reagents i Co 2 (CO) 8 NMO 16 equiv.N-methylmorpholineN-oxide. Better diastereoselectivity has been obtained by carrying out asymmetric Pauson–Khand reactions on a carbohydrate template.447 The use of a chiral ligand on cobalt to induce asymmetry is an attractive alternative approach but requires routes to unsymmetrical Co 2 (CO) 5 L complexes. Amine Noxide448 and photochemical449 methods have been described. Solid-phase supports have been used for the Pauson–Khand reaction,450 and photochemical451 and chemical (CF 3 CO 2 H)452 promotion have been examined. Applications to polyquinane synthesis have exploited the phenylcyclohexanol auxiliary illustrated in 97.453 In a tandem approach two Pauson–Khand reactions have been performed back-to-back in the cyclisation of 98,454 and sequentially with 99.455 The Pauson–Khand process can be interrupted by allowing oxygen to intervene.The intramolecular case a§ords monocyclic enones in place of the normal bicyclic products.456 O O Me3Si 98 OSiMe3 99 SiMe3 Cyclopentadienylcobalt chemistry oligomerisation combined with complexation The cyclotrimerisation of two alkynes and an alkene produces a diene cobalt complex with the diene at the location corresponding to the original alkynes. Under thermodynamic conditions with strained products rearrangement can occur as in the formation of 100 (Scheme 36). The factors influencing selectivity have been examined. 457 Rearrangement is also required to account for 101 which is formed together with a metal-free structure with an exocyclic double bond.458 Enynes have been cyclised to a§ord exocyclic 1,3-dienes their g4-complexes and structures in which the metal-bound region has moved into the ring.459 Cobalt is not the only metal that can be employed.g1-Mn(CO) 4 complexes have been elaborated by insertion of alkynes to provide intermediates that are eventually converted into metal-complexed pyrylium salts.460 Pentacarbonylchromium carbene chemistry the Do� tz reaction Double Do� tz cyclisation with a butadiyne gives a 23% yield of the chiral binaphthyl structure 102 which is formed as a single isomer (Scheme 37).461 Precursors for conventional biaryl formation have been obtained by an application of the Do� tz 223 Organometallic chemistry the transition metals CoCp CoCp 100 C O O But O O CoCp But 101 i i Scheme 36 Reagents i CpCo(CH 2 –– CH 2 ) 2 O O (CO)5Cr Cr(CO)5 Me Me HO Ph O O Me Me Ph OH 102 i Scheme 37 Reagents i PhC–– – C-C–– – CPh THF reaction.462 Cyclisation with prop-2-ynyl alcohols can be modified to a§ord lactones.463 The Do� tz cyclisation initially forms an g6-arene complex. Such products can themselves be important intermediates (see above) and there has been an extensive investigation of their isolation by in situ trapping of the phenol with silylating reagents. 464 Products of this type include naphthalenes with cyclopropyl groups next to the chromium-bound arene,465 and unusually substituted indole complexes.466 Indolines have also been obtained.467 Just as the Pauson–Khand reaction can be interrupted so too can the Do� tz process which makes five-membered rings when intercepted before the carbonyl insertion. In the case reported468 tautomerisation not oxidation interrupts the reaction.3 Organometallic compounds New applications of organometallic complexes Organometallic rods and dipoles Some striking structures have been reported this year with long oligoalkyne rods linking organometallic centres. The crystal structure of the tetrayne 103 shows ferro- 224 G.R. Stephenson FeCp FeCp FeCp N W(CO)4PPh3 103 104 Me Me Me Me Me Fe PPh2 Ph2P Me Me Me Me Me Ph2P PPh2 Fe + 105 Cp(CO)3W W(CO)3Cp 106 Cp1 2Ti FeCp FeCp Pt Et3P Et3P Pt PEt3 PEt3 109 108 C C Ru Ph2P PPh2 Ru Me Me Me Me Me Me Me Me Me Me Ph2P PPh2 107 C C FeCp FeCp FeCp FeCp FeCp FeCp 110 + 225 Organometallic chemistry the transition metals cenyl groups pointing both up and down. The W(CO) 4 PPh 3 pyridine adduct 104 has mixed alkene–arene link and in the corresponding 4-pyridyltriyne the crystal structure showed large thermal ellipsoids at the second sp carbon out from the pyridine ring.469 Direct attachment of the tetrayne to metals is also possible and in 105 mie FeII–FeIII centres are linked to form a structure described as a ‘molecular wire’ with the strongest electronic coupling through nine bonds observed to date.470 Some long structures of this type are easily made.Two Cp(CO) 3 W–C–– – C–C–– – C–H units are linked in 85% yield by oxidation with Cu(tmeda)Cl/O 2 to form 106. The same building block with PtCl 2 (dppe) forms a bent rod with Pt(dppe) in the centre.471 The same bent structure is encountered in a quite di§erent trimetal complex 107 which when oxidised with Ag` is converted via a bis-ferrocenium species into 103 and Cp@2 Ti2` in 90–98% yield.472 The unusual organic link in 108 was introduced by direct complexation of the pentayne with PtCl 2 (Et 3 P) 2 .473 Bending at carbon is introduced when a methine link is present in the chain as in 109.This complex originates from HC–– – C–CHOH–C–– – CH and a ruthenium chloride complex which are joined by AgBF 4 .474 The drawing of 109 represents one of two equivalent canonical forms. The issue of bonding in polyalkyne substructures in organometallic complexes has been addressed in a treatment that relates to a hypothetical organometallic net which has a degree of complexity that currently transcends synthetic capabilities.475 Allenes are interesting links because they introduce a twist into structures as in 110 which is isolated in low (4%) yield from triferrocenylallenium tetrafluoroborate.476 When three carbons are bound end-on to a metal the allene motif becomes an allenylidene ligand.In 111 two allenylidene g1-ruthenium complexes are joined by thiophene. This is a dication but the mixed RuII–RuI structure is accessible electrochemically. 477A 2,5-dialkynylthiophene has been used to joinMoand Fe centres in bis g1-complexes.478 Other links include anhydrides,479 Me 2 SiOSiMe 2 ,480 COMe481 and PPh 2 .482 This last case features a Co 2 (CO) 6 complexed alkyne as a substituent at phosphorus. The analogous CH-linked (prop-2-ynyl) situation has been examined with bis-CpMo(CO) 2 in a cationic structure.483 Linking by CH 2 interrupts the conjugation but a more extended range of structures has been reported in this series.The polymetallic prop-2-ynylferrocene structures have been combined in hexametal dimers by joining the CH 2 positions. Alternatively both Cp rings in ferrocene can carry prop-2-ynyl complexes and in one case these too have been joined.484 Larger clusters are combined by a variety of strategies.485–487 In 112 the cluster metallates pyridine producing a more direct attachment than in 104.487 Alkene and diene links lie between a Cr(CO) 3 arene complex and cationic arene or thiophene complexes of Mn(CO) 3 .488 An alkene between Cp ligands is transformed into the CH–CH connection between pentfulvadiene ligands by oxidation of Ru(C 5 Me 5 ) centres.489 Short links can illustrate important issues. The simple ferrocenylethynyllithium or its Ru counterpart can be combined with MnBr(CO) 5 to give bimetallic structures.490 The corresponding ferrocene with CpFe(dppm) in place of Mn(CO) 5 has been oxidised to give another example of a mixed valence complex.491 The mixed valence/canonical form issue is encountered with a three atom (cyclobutenyl) link in a bis-CpFe(CO) 2 complex and its (C 5 Me 5 )ReNO(PPh 3 ) counterpart.492 A 1,3-bisalkynylcyclobutadiene tricarbonyliron complex has been described in the continuation of the Bunz group’s remarkable work towards highly elaborate polyorganometallic assemblies.493 The possibility of nonlinear optical (NLO) properties in bimetallic structures with 226 G.R.Stephenson FeCp S C C Ru Cl Ph2P PPh2 Ph2P PPh2 C C Ru Cl PPh2 Ph2P PPh2 Ph2P 111 N Ru(CO)3 (CO)2Ru Ru(CO)4 H 112 Cr+(CO)3 FeCp BF4 – Cp(PMe3)2Ru NO2 113 114 Mn(CO)3 – – – – – 115 2+ conjugation through the link is a major motivation in this field of research (e.g.Tessier Youngs et al.,473 Dixneuf et al.,477 Fischer et al.,492 Cooke and Schultz,494 Toma et al.495). There are now excellent examples. Neutral and cationic metal centres are combined in 113 giving good polarisability and polarisation to the p-system and a very high hyperpolarisability (b\570]10~30 esu) measured by hyper-Rayleigh scattering.496 The parameter b is a useful measure of success because it is determined in solution and so does not su§er from complications di§erences in crystal form. Fieldinduced second-harmonic generation (EFISH) is another important technique. Even monometallic structures can give large values of kb e.g. 9700]10~48cm5 esu~1 for 114 in which Cp(PMe 3 ) 2 RuCCC 6 H 4 C–– – C– has been introduced497 in place of the ferrocene of Green’s original NLO organometallic.Considerable e§ort has been devoted to these lengthened systems.498 Another variant of the Green compound has a CH 2 OCH 2 strap to disturb the parallel planes of the two Cp rings.499 The role of the nitroarene is simply as a polarisable electron withdrawing group. A 4-substituted N-methylquinolinium ion has been used for this purpose giving improved hyperpolarisability and EFISH measurements.500 A dimethylazulene has also been put at this position.501 NLO measurements on structures containing individual end-groups from the more elaborate assemblies 103–113 o§er a guide to separate contributions of organometallic and metallo-organic (i.e. heteroatom linked) moieties.NLO properties have been reported for Schi§-base complexes of Ni Zn and Cu,502 Pt(polyyne) (PPY),503 nickel dithiolene complexes,504 and molybdenum or tungsten clusters with copper or sil- 227 Organometallic chemistry the transition metals ver.505 Measurements have also been made on metallo-organic thin films.506 (For more examples of thin film structures see the next section of this Report.) Metallo-organic links through two tripyrazol-1-yl borate substituents have joined two ferrocenes with a third iron atom.507 PdCl 2 bound by two substituted pyridines also fulfils this role.508 A nitrile has linked iron and molybdenum centres in a paramagnetic structure.509 Some eye-catching monometallic structures have been reported. The first linear Ph 2 C–– C––C––C––C–– iridium complex was described,510 and vinylidene complexes of manganese have cyclic tetra- or hexa-silanes at the end of the C––C unit not attached to the metal.511 Two studies of sesquifulvalene complexes from Tamm’s group explore stabilisation e§ects.512,513 Monometallic analogues of 113 were reported.These had Mn(CO) 3 Mn(CO) 2 P(OMe) 3 and Mn(CO) 2 (PPh 3 ) groups in place of FeCp and a metal-free tropylium cation at the other end of the alkyne.511 Resonance e§ects in canonical structures were examined and b values were reported though these were a factor of ten smaller than that of 113. With so many metals and ligands available to choose from a great many di§erent structural forms are available. Three-,514,515 four-,516,517 five-516 and six-armed518 structures with the metals on the outside,514–516 or the centre,516–518 ranging from monocations514,517,518 to the remarkable pentaanion 115,516 illustrate this point.The pentalithium salt prepared quantitatively from a pentacyclopentadiene derivative with butyllithium in THF is itself a potentially important building block for still greater structures. At the opposite extreme metals can be pressed close together when they share a ligand,519–521 or when the ‘ligand’ that joins them is composed of two directly linked ‘classic ligands’ as in bis-Cp,522–524 and aryl-Cp525 structures. Some structures of this type contain important metal–metal bonds that can be manipulated (broken and re-formed) without loss of the metals from the ligand.522–524 Organometallic liquid crystals films and dendrimers Ferrocene is still the most popular organometallic moiety for applications in liquid crystals and micelles.Often it is chosen because of its extreme stability and its well understood organic chemistry. Attention is now turning to the exploitation of the redox chemistry of the ferrocene group and here unique benefits for the inclusion of organometallic units can be anticipated. Oxidation of a neutral and hence non-polar nonamethylferrocene head-group in a rod-like structure has been used to place a cation at the end of the rod promoting the formation of a smectic A phase. The product 116 is the first ferrocenium-containing thermotropic liquid crystal.526 With ferrocene groups at both ends of a linker oxidation now gives rise to vesicle formation. 527 Electrochemistry was used to determine that both head-groups had been oxidised and is consistent with a spacing between the groups of about 20 Å in vesicles formed with 117.Similar results were obtained with a rigid steroid as the link but were distinct from results with a single ferrocene on a long alkyl chain. The electrochemistry of aryl diether-linked ferrocenium ions has been examined.528 Two long alkyl chains have been attached to ferocene in 118 which contains 1,3-dicarbonyl units in the enol form.529 Bis(arylimino)ferrocenes have also been examined,530 and with amide-linked amino acid esters as the substituents ordered conformations are observed.531 Chemistry that manipulates mono- and di-substitution on ferrocene will pave the way for more ambitious liquid crystal structures. 228 G.R. Stephenson FeC5Me5 O O O O O + FeCp O + O FeCp + 116 117 TsO– Ferrocene and isoquinolinium groups linked by a rigid 9,10-diarylnaphthalene centre form inverse micelles and Langmuir–Blodgett films with non-centrosymmetric Z-type layers.532 Two ferrocenes linked with unsaturated rigid spacers o§er a more disk-like structure.The example 119 forms Langmuir monolayers on the surface of water.533 Metal carbonyls can also be applied in work of this type. The tricarbonylchromium chloresteryl benzoate complex and the corresponding tricarbonyliron hexadienoate derivative 120 are cholesteric mesogens.534 In the tricarbonylchromium case the complex exhibited its mesophase at a lower temperature than the free ligand.535 A tricarbonylchromium group has been placed at the centre of a much longer and more flexible rod combining arene and long-chain alkyl components with imine ester and ether links.Smectic C and nematic phases have been observed.536 The repeat unit 121 lies at the surface of an organometallic fourth generation dendrimer containing all 48 ruthenium atoms in the surface layer.537 As many as 64 ferrocenes occupy the surface of a poly(propylenimine) dendrimer.538 Organometallic polymers Linking ferocenes by monosubstitutions on each ring can produce structures with the iron atoms within in the polymer chain. Alternating ferrocene and SiMe 2 units have been combined in this way.539 With SiMeCl in the repeat unit the polymer can be elaborated after formation.540 SnMe 2 -541 and S 2 -542 linked polymers have also been described as have the Se 2 - and Te 2 - linked counterparts.542 In 122 a rigid rod is combined with ferrocene and (PBu 3 ) 2 Pd centres.The palladium centre and a Ru(dppe) 2 centre have been joined in polymers by acetylide links developed from HC–– – C–C 6 H 4 –C–– – CH.543 This same acetylide strategy has been employed with –(C–– – C) 2 –C 6 H 4 –(C–– – C) 2 – as the linker.544 A cymantrene-containing organometallic polymer has been made by Suzuki coupling.545 When the connection is by two substitution sites on one ligand the metal stands aside from the chain as in the tetrayne-linked oligomer 123.546 An unusual polymerisation exploits thermally induced loss of methane to form the polymeric zirconacycle 124.547 Gold,548 manganese549 and platinum550 have been inserted directly into the polymer backbone by a variety of techniques e.g. coordination by pyridine,548 in Schi§ base complexes,549 and much more weakly linked hydrogen bonded structures.550 Conventional polymers can be elaborated to introduce ligand sites for complexation.229 Organometallic chemistry the transition metals Fe O O H O O H 118 Fe Fe O O O chloresterol O Fe(CO)3 119 120 O O O Ru(CO)2Cp Ru(CO)2Cp 121 PBu3 Pd PBu3 Fe n 122 Me3Si Me3Si CoCp n 123 230 G.R. Stephenson SiMe3 Cp2Zr Me Zr Me3Si Cp Cp n i 83% 124 Scheme 38 Reagents i heat Cyclopentadiene introduced onto a polystyrene support has been complexed by rhodium.551 Polymethacrylates from copolymerisation carry ferrocene-containing thermotropic liquid crystal side-chains.552 Peptides are rather specialised polymers but since they can be made on supports it is possible to develop exotic supported catalysts with ligand sites introduced on unnatural amino acids themselves built up on resin beads.The key is the use of phosphine sulfides to protect phosphine ligands from oxidation during solid phase synthesis.553 Ru Rh and Pd complexes have been immobilised on solid supports.554 Both these and the peptide-based systems have been shown to be functional hydrogenation catalysts. A polymer-modified electrode with Rh(C 5 Me 5 ) complexes has been prepared.555 Organometallic sensors and receptors Selectivity in response to dihydrogen phosphate makes the diferrocene derivative 125 an exceptional sensor. This selective luminescent anion sensor shows a 20-fold increase in emission intensity at 690nm when the analyte is bound in the diamide pocket.556 Less selective neutral ferrocene-based anion receptors have also been shown to bind dihydrogen phosphate.557 Chiral recognition of camphor-10-sulfonate has been achieved with a cobaltocenium-based receptor.558 Work with crown ether binding sites continues.Electrochemical sensing of sodium and magnesium ions has been studied with a di(aminobenzo)crown equipped with two ferrocene carbaldehydes attached by Schi§ base links.559 A cobaltocenium structure links two indenyl ligands with azacrown ethers as substituents. Complexation of lithium and sodium is studied by cyclic voltametry.560 The same indenyl azacrown as a tricarbonylmanganese complex allows the detection of binding of alkali metal ions by FTIR although the shifts are small. A much larger shift is observed upon protonation of the nitrogen. Protonation e§ects of this type have been developed for use in IR-active organometallic pH probes.Since the vibrational bands are narrow and intense several independent responses can be measured in the same spectroscopic experiment allowing dual or multiple sensing.561 This IR-readout approach has also been developed to detect p-stacking of aromatic rings and the binding of organic analytes in crowns by ammonium ion recognition.562 A cyclic tetramer with two ferrocenes and two decaalkylferrocenes in the ring has been prepared.563 The same paper reports the formation of the monocobalt analogue 126. Complexation of cobalt between two cyclopentadienes strategically placed at the ends of a trimer of ferrocene-based building blocks closes the ring. Two ferrocenes have been placed at opposite sides of a polycyclic macrocycle with diazacrowns joining pairs of cyclopentadienyl ligands.564 A rigid aromatic hydrophobic pocket has been 231 Organometallic chemistry the transition metals Fe N N (bipy)2Ru O NH FeCp O NH FeCp 125 Me Me Me Me Me Me Me Me Co Me Me Me Me Me Me Me Me Fe + PF6 – 126 Fe 2+ closed with a ferrocene attached by an amide on each ring.565 The opposite is achieved in ferrocene-closed ring containing four pyrazoles.566 An alternative structure was also prepared in which a tertiary amine closed the ring but two of the pyrazoles bore ferrocenes as substituents.Four ferrocenes have been attached to a porphyrin at the methines joining the pyrroles. The tetraruthenocenyl analogue and a corresponding metal carbonyl structure with four tricarbonylmanganese centres have also been prepared.567 Receptors are not only important in analytical chemistry; e¶cient recognition of specific features is also pertinent to selective catalysis and organometallic structures have a role to play here too.An azacrown system with a ferrocenyldiphosphine ligand as a substituent has been used in enantioselective allylation.568 Bioorganometallic chemistry A ferrocenyl derivative of hydroxytamoxifen has been prepared as an estradiol receptor site-directed cytotoxic agent and tested against a human breast cancer cell line.569 In a continuation of work on steroid-based compounds the aryloxy group of 17-a- ethynylestradiol has been derivatised with an MeC 6 H 4 FeCp marker but in this case a¶nity for the receptor was lost.570 Oxorhenium metallo-organic estradiol-derived compounds have been prepared,571 and two strategies for metal containing steroid look-alikes have been described.572,573 Supramolecular Rh(C 5 Me 5 ) nucleoside and nucleotide complexes have been used in molecular recognition studies with amino acids.574 Organocobalt complexes have been developed for selective tagging of biological macromolecules by exploiting the chemistry of amino ester substituents,575 or other activated esters.576 Peptide hydrolysis has been promoted by platinum and palladium complexes.577 The radionuclide technetium-99 has been incorporated into peptides with a high a¶nity for the somatostatin receptor.578 The chemistry of ferrocene building blocks The increased focus on ferrocene derivatives in new applications has revitalised e§orts in the oldest branch of organometallic chemistry.Making unsymmetrical CpFeCp@ 232 G.R. Stephenson structures,579 or selectively substituted rings in symmetrical forms,580 will open the way to new functionalised systems. In the latter case enol ethers provide the source for the cyclopentadienyl rings. A conventional acylation strategy has been used to introduce perfluoroalkyl chains.581 Monolithiation of ferrocene is a di¶cult problem. A revised procedure has been o§ered.582 Mono-bromine–lithium exchange with 1,1- dibromoferrocene constitutes an alternative.583 Chloromethylenetriphenylphosphonium ylide e§ects an alkenylation of ferrocene carbaldehyde to a§ord a mixture of E- and Z-isomers that can be converted without separation into ethynylferrocene by treatment with butyllithium.584 An ingenious trick allows temporary attachment of a diamine to ferrocene carbaldehyde to relay metallation to the unsubstituted ring.585 Asymmetric functionalisation is important if the goal is a ligand for use in asymmetric synthesis.Approaches based on metallation directed by chiral auxiliaries are popular. Metallation in the presence of chiral oxazoline substituents has been followed by trapping with Me 3 Si,586 Bu 3 Sn,587 and Ph 2 PCl.588 The combination of sparteine with a ferrocene carboxamide also gives good ee values in the induced planar chirality. 589 A chiral 1,2-diamine with a dimethylaminomethyl substituent on the ferrocene was less e§ective but in this case trapping with DMF introduced a formyl group.590 Chirality in side-chains is also valuable. (S)-1-Amino-2-methoxymethylpyrrolidine has been used to form chiral ferrocenylalkylamines.591 Asymmetric reduction of diacyl ferrocenes is also e§ective.592 Functional changes in side-chains include replacement of OH in CH 2 OH by reaction with triphenylphosphite to form a phosphonate,593 aldol functionalisation of acylferrocene with aromatic aldehydes (a reaction performed in the presence of cyclodextrin which induced a slight asymmetric bias),594 and Lewis acid catalysed displacement of OMe from CH 2 OMe substituents.595 Organometallic complexes as ligands Many bimetallic structures both with separated metals and with metal–metal bonding can be regarded as containing organometallic structures as ligands but the description is of greatest value when applied to organometallic auxiliaries that are employed as ligands in other processes most typically asymmetric catalysis.There is an increasingly large number of examples and ligands of this type o§er geometries which may be advantageous and will certainly be unusual. The use of the aminophosphine 127 as a ligand in Grignard cross-coupling,596 or the diamine 128 in asymmetric hydrosilylation,597 provide typical examples. Levels of asymmetric induction can be very high. (S)-DIPOF 129 gives 96% ee in a quantitative asymmetric hydrosilylation catalysed by [Ir(COD)Cl] 2 .598 The ligand 130 has been used in asymmetric palladium catalysed allylic substitution.599 More elaborate ligands can provide more than one binding site. This seems likely to be a growth area in future years because of the extra benefit of holding catalyst and substrates together with separate recognition features.With an aminoalkyl substituent to dock an alkene substrate with an organoboron centre in 131 an intermolecular hydrogenation or hydroformylation can be rendered intramolecular.600 Organometallic mechanisms C–H activation in methane has been studied by perturbation and hybrid density functional theory comparing Co Rh and Ir. Only the Rh and Ir complexes should be reactive towards alkanes.601 Oxidative addition of methane to palladium clusters has 233 Organometallic chemistry the transition metals CpFe NMe2 PPh 127 Me N Se Se CpFe CpFe N Me 128 N O Ph Ph Ph2P 129 CpFe Fe CO2Me PPh2 CO2Me PPh2 130 Fe PPh2 PPh2 N B O Me Me 131 also been examined.602 Reductive elimination of C–H from ruthenium clusters changes from a CO-associative mechanism to a CO-dissociative mode when other ligands are varied.603 An alkane-associative mechanism has been identified in the activation of cyclooctane by IrClH 2 (Pr* 3 P) 2 to form cyclooctene.604 Hydrogen migration in Ir–ketene complexes has been shown by NMR to proceed in a stepwise fashion.605 Non-linear temperature dependence has been observed in asymmetric hydrogenation.606 A mechanism for arene exchange in g6-rhodium complexes involves a square planar cis-phosphine cis-ether intermediate a conclusion based on NMR EXSY experiments.607NMR is a powerful tool for mechanism research 19F–19F COSY has given evidence for g2-arene intermediates on the way to C–H and C–F insertion products.608 para-Hydrogen induced polarisation has allowed the detection of intermediates at low concentrations in a study of ligand exchange in iridium complexes.609 Femtosecond IR experiments allowed the direct observation of a reactive solvated monocarbonyl intermediate in C–H activation by a rhodium complex.610 Time-resolved IR spectroscopy makes good use of the IR time-scale and has been applied to the photochemical rearrangement of a dirhenium MeO 2 CC–– – CCO 2 Me complex in which the ligand spans the rhenium atoms.Evidence was obtained for a bis-carbene intermediate.611 Palladium catalysed alkene dimerisation has been studied.612 and mass transfer of ethylferrocene from water to a droplet has been shown to be limited by di§usion. In contrast,OHor NMe 2 groups on the alkylferrocene were also governed by adsorption at the interface. Electrochemical methods were used in this investigation.613 234 G.R.Stephenson A kinetic study of the Tebbe reaction supports the role of Cp 2 Ti––CH 2 as the reactive species.614 Kinetics have been applied to the transfer of tricarbonyliron between benzylideneacetone and azadienes.615 In some cases calculations o§er the best guide. Nucleophile addition to g3-palladium complexes,616 hydrogen exchange coupling in Cp 2 MoH 3 ,617 and isomerisation of osmium hydride complexes have been subjected to ab initio treatments.618 Molecular mechanics calculations have been applied to properties of iron acyl complexes.619 Organometallic structures and bonding C 60 is undoubtedly an eye-catching ligand. The lattice dynamics and hyperfine interactions of its Fe(CO) 4 complex have been reported.620 Extending out from C 60 provides larger ligand sites and an Fe(CO) 3 adduct has been prepared in this way.621 An unusual small ligand in 132 contains a run of cumulated carbon atoms.622 This is reminiscent of the rod structures discussed earlier except that the metal is bound side-on.C–C links between metals have also been the subject of structural study.623 Three PC–– – NPr* 2 units are combined in the unusual nickel complex 133.624 This complex contained a side-on P–– – C triple bond. A P–– – C double bond is coordinated in 134.625 C C C C Ph Ph Ph Ph Pri 3P Rh Cl PPri 3 P C NPri 2 Ni P P Pri 2N NPri 2 132 133 P (CO)2W Me Ar Cp 134 Co 2 (CO) 6 is an important fragment. It has been stabilised by a bridging ligand in 135. Carbon monoxide scrambling in 135 has been examined.626 Charge stabilisation is the issue in the dication 136,627 and the di(azulenyl)ferrocenylcarbenium ion 137.628 Three di§erent aromatic substituents are present in the pyrylium complex formed from 138.629 Bond-lengthening in dihydrogen complexes,630 linkage isomerism in o-xylylene complexes,631 aromatic ring currents in bis-Cr(CO) 3 complexes of dibenzannulene632 and hapticity interconversion in cycloheptatrienyl complexes633 illustrate other contemporary structural issues.Correlation of Hammett constants with NMR chemical shifts is useful with 1-aryl substituted palladium allyl complexes.634 Ligand e§ects on reactivity have been examined,616 and a theoretical study probed the influence of ancillary ligands.635 The final citation in this section identifies a feature article that may herald a new age in organometallic chemistry. Issues of intermolecular interactions and supramolecular organisation take the subject beyond its normal bounds.With great structural variety and increasingly well understood functional utility available in organometallic solids examining how they organise together is likely to grow into a major field supraorganometallics. 636 Note This will be the last year of this catch-all survey of the organic chemistry of the transition elements. The subject has now become too large. When the 1997 literature is 235 Organometallic chemistry the transition metals O P P (CO)2Co Co(CO)2 O O 135 (CO)2Mo Mo(CO)2 H2C CH2 + + 2 BF4 – 136 + FeCp PF6 – 137 O CF3 Cl Mn(CO)3 138 reviewed separate Reports on catalytic and stoichiometric bond-formation and structural/ mechanistic aspects of organometallic chemistry will be presented.The organisation of material in this 1996 Report looks ahead to the need to review these features independently. References 1 Y. Hamada N. Seto H. Ohmori and K. Hatano Tetrahedron Lett. 1996 37 7565. 2 N. Nomura Y. C. Mermet-Bouvier and T. V. RajanBabu Synlett 1996 745. 3 P.A. Evans and T. A. Brandt Tetrahedron Lett. 1996 37 9143. 4 G. Brenchley M. Fedoulo§ E. Merifield and M. Wils Tetrahedron Asymmetry 1996 7 2809. 5 G. Zhu M. Terry and X. Zhang Tetrahedron Lett. 1996 37 4475. 6 A. Togni U. Bruckhardt V. Gramlich P. S. Pregosin and R. Salzmann J. Am. Chem. Soc. 1996 118 1031. 7 W. Zhang T. Hirao and I. Ikeda Tetrahedron Lett. 1996 37 4545. 8 P. Barbaro A. Currao J. Herrmann R. Nesper P. S. Pregosin and R. Salzmann Organometallics 1996 15 1879. 9 E. Pen8 a-Cabrera P.-O.Norrby M. Sjo� gren A. Vitagliano V. De Felice J. Oslob S. Ishii D. O’Neill B. A ! kermark and P. Helquist J. Am. Chem. Soc. 1996 118 4299. 10 C. Bolm D. Kaufmann M. Zehnder and M. Neuburger Tetrahedron Lett. 1996 37 3985. 11 P. E. Blo� chl and A. Togni Organometallics 1996 15 4125. 12 M. Widhalm P. Wimmer G. Klintschar J. Organomet. Chem. 1996 523 167. 13 B.M. Trost and R. C. Bunt J. Am. Chem. Soc. 1996 118 235. 14 B.M. Trost and R. C. Brunt Angew. Chem. Int. Ed. Engl. 1996 35 99. 15 B.M. Trost M. J. Krische R. Radinov and G. Zanoni J. Am. Chem. Soc. 1996 118 6297. 16 G. Koch and A. Pfaltz Tetrahedron Asymmetry 1996 7 2213. 17 M. Sawamura M. Sudoh and Y. Ito J. Am. Chem. Soc. 1996 118 3309. 18 A. H. Kubota and K. Koga Heterocycles 1996 42 543. 19 B.M. Trost A. C. Krueger R.C. Bunt and J. Zambrano J. Am. Chem. Soc. 1996 118 6520. 20 B.M. Trost and R. C. Lemoine Tetrahedron Lett. 1996 37 9161. 21 J. F. Bower and J. M.J. Williams Synlett 1996 685. 22 M.T. Crimmins and B. W. King J. Org. Chem. 1996 61 4192. 236 G.R. Stephenson 23 T. Hayashi M. Kawatsura H. Iwamura Y. Yamaura and Y. Uozumi Chem. Commun. 1996 1767. 24 E. B. Koroleva and P. G. Andersson Tetrahedron Asymmetry 1996 7 2467. 25 I. Shimizu Y. Matsumoto K. Shoji T. Ono A. Satake and A. Yamamoto,Tetrahedron Lett. 1996 37 7115. 26 B.M. Trost and Z. Shi J. Am. Chem. Soc. 1996 118 3037. 27 B.M. Trost R. Madsen S. G. Guile and A. E. H. Elia Angew. Chem. Int. Ed. Engl. 1996 35 1569. 28 M.J. Konkel and R. Vince J. Org. Chem. 1996 61 6199. 29 D. R. Deardor§ K. A. Savin C. J. Justman Z. E.Karanjawala J. E. Sheppeck II D. C. Hager and N. Aydin J. Org. Chem. 1996 61 3616. 30 L. B. Akella and R. Vince Tetrahedron Lett. 1996 52 2789. 31 V. K. Aggarwal N. Monteiro G. J. Tarver and S. D. Lindell J. Org. Chem. 1996 61 1192. 32 N. Vicart J. Gore� and B. Cazes Synlett 1996 850. 33 S. Thorimbert and M. Malacria Tetrahedron Lett. 1996 37 8483. 34 C. Goux P. Lhoste D. Sinou and A. Masdeu J. Organomet. Chem. 1996 511 139. 35 S. G. Pyne and Z. Dong J. Org. Chem. 1996 61 5517. 36 D.M. David G. W. O’Meara and S. G. Pyne Tetrahedron Lett. 1996 37 5417. 37 R. C. Larcock T. R. Hightower L. A. Hasvold and K. P. Peterson J. Org. Chem. 1996 61 3584. 38 Z. Jin and P. L. Fuchs Tetrahedron Lett. 1996 37 5253. 39 A.M. Castan8 o M. Ruano and A. M. Echavarren Tetrahedron Lett. 1996 37 6591. 40 F.Le Bideau F. Gilloir Y. Nilsson C. Aubert and M. Malacria Tetrahedron. 1997 53 7487. 41 M. Sakamoto I. Shimizu and A. Yamamoto Bull. Chem. Soc. Jpn. 1996 69 1065. 42 Y. Takemoto S. Kuraoka T. Ohra Y. Yonetoku and C. Iwata Tetrahedron. 1997 53 603. 43 M. Suginome A. Matsumoto and Y. Ito J. Am. Chem. Soc. 1996 118 3061. 44 V. Michelet I. Besnier and J. P. Gene� t Synlett 1996 215. 45 J. V. Allen and J. M. J. Williams Tetrahedron Lett. 1996 37 1859. 46 S. Watanabe T. Fujita M. Sakamoto T. Ikeda and T. Haga J. Essent. Oil Res. 1996 8 29. 47 S. Lemaire-Audoire M. Savignac and J. P. Gene� t Synlett 1996 75. 48 S. Sigismondi and D. Sinou J. Chem. Res. (S) 1996 46. 49 O. Loiseleur P. Meier and A. Pfaltz Angew. Chem. Int. Ed. Engl. 1996 35 200. 50 T. Kamikawa Y. Uozumi and T. Hayashi Tetrahedron Lett.1996 37 3161. 51 S.-K. Kang H.-W. Lee S.-B. Jang T.-H. Kim and S.-J. Pyun J. Org. Chem. 1996 61 2604. 52 A. Tenaglia and F. Karl Synlett 1996 327. 53 S. Cacchi P. G. Ciattini E. Morera and P. Pace Synlett 1996 545. 54 C. A. Busacca and Y. Dong Tetrahedron Lett. 1996 37 3947. 55 G. T.Crisp and M. G. Gebauer Tetrahedron Lett. 1996 52 12 465. 56 L. Ripa and A. Hallberg J. Org. Chem. 1996 61 7147. 57 C. Senesson M. Larhed C. Hyqvist and A. Hallberg J. Org. Chem. 1996 61 4756. 58 S. Sengupta and S. Bhattacharyya Synth. Commun 1996 26 231. 59 Y. Nishibayashi C. S. Cho and S. Uemura J. Organomet. Chem. 1996 507 197. 60 H. Matsuhashi Y. Hatanaka M. Kuroboshi and T. Hiyama Heterocycles 1996 42 375. 61 K. S. Gudmundsson J. C. Drach and L. B. Towsend Tetrahedron Lett. 1996 37 6275.62 S. Lemaire-Audoire M. Savignac C. Dupuis and J.-P. Gene� t Tetrahedron Lett. 1996 37 2003. 63 C. Montalbetti M. Savignac J.-P. Gene� t J.-M. Roulet and P. Vogel Tetrahedron Lett. 1996 37 2225. 64 D. L. Comins S. P. Joseph and Y.-M. Zhang Tetrahedron Lett. 1996 37 793. 65 K. A. Beaver A. C. Siegmund and K. L. Spear Tetrahedron Lett. 1996 37 1145. 66 S. Hillers and O. Reiser Chem. Commun. 1996 2197. 67 S. Hilliers S. Sartori and O. Reiser J. Am. Chem. Soc. 1996 118 2087. 68 D. E. Kaufmann M. Nouroozian and H. Henze Synlett 1996 1091. 69 T. Je§ery Tetrahedron Lett. 1996 52 10 113. 70 M.T. Reetz and G. Lohmer Chem. Commun. 1996 1921. 71 M.T. Reetz R. Breinbauer and K. Wanninger Tetrahedron Lett. 1996 37 4499. 72 I. E. Pop C. F. Dhalluin B. P. De� prez P. C. Melnyk G. M. Lippens and A.L. Tartar Tetrahedron Lett. 1996 52 12 209. 73 J. M. Brown and K. K. Hii Angew. Chem. Int. Ed. Engl. 1996 35 657. 74 C. Amatore E. Carre� A. Jutand H. Tanaka Q. Ren and S. Torii Chem. Eur. J. 1996 2 957. 75 K. Nishi Y. Narukawa and H. Onoue Tetrahedron Lett. 1996 37 2987. 76 M.E. Kuehne T. Wang and P. J. Seaton J. Org. Chem. 1996 61 6001. 77 Y. Miki Y. Tada N. Yanase H. Hachiken and K.-I. Matsushita Tetrahedron Lett. 1996 37 7753. 78 W. Deng M.S. Jensen L. E. Overman P. V. Ryucker and J.-P. Vionnet J. Org. Chem. 1996 61 6760. 79 Y. Yokoyama K. i and Y. Murakami Tetrahedron Lett. 1996 37 9309. 80 J. W. Benbow and B. L. Martinez Tetrahedron Lett. 1996 37 8829. 81 P. Galda and M. Rehahn Synlett 1996 614. 82 D. J. P. Pinto R. A. Copeland M. B. Covington W.J. Pitts D.G. Batt M. J. Orwat G. N. Lam A. Joshi Y.-C. Chan S. Wang J. M. Trzaskos R. L. Magolda and D. M. Kornhauser Bioorg. Med. Chem. Lett. 1996 6 2907. 237 Organometallic chemistry the transition metals 83 H. Zhang F. Xue T. C. W. Mak and K. S. Chan J. Org. Chem. 1996 61 8002. 84 H. Zhang and K. S. Chan Tetrahedron Lett. 1996 37 1043. 85 A. Godard P. Rocca V. Pomel L. Thomas-dit-Dumont J. C. Rovera J. F. Thaburet F. Marsais and G. Que� guiner J. Organomet. Chem. 1996 517 25. 86 F. Guillier F. Nivoliers C. Cochennec A. Godard F. Marsais and G. Que� guiner Synth. Commun. 1996 26 4421. 87 B. Joseph B. Malapel and Y.-Y. Me� rour Synth. Commun. 1996 26 3289. 88 T. Sakamoto Y. Kondo S. Sato and H. Yamanaka J. Chem. Soc. Perkin Trans. 1 1996 459. 89 R. D’Alessio and A. Rossi Synlett 1996 513.90 T. Ishiyama T.-A. Ahiko and N. Miyaura Tetrahedron Lett. 1996 37 6889. 91 G. Desurmont S. Dalton D.M. Giolando and M. Srebnik J. Org. Chem. 1996 61 7943. 92 J. P. Hildebrand and S. P. Marsden Synlett 1996 893. 93 Y. Narukawa K. Nishi and H. Onoue Tetrahedron Lett. 1996 37 2589. 94 S. D. Brown and R. W. Armstrong J. Am. Chem. Soc. 1996 118 6331. 95 J. W. Guiles S. G. Johnson and W.V. Murray J. Org. Chem. 1996 61 5169. 96 S.-K. Kang H.-W. Lee S.-B. Jang and P.-S. Ho J. Org. Chem. 1996 61 4720. 97 S. Darses T. Je§ery and J.-P. Gene� t J.-L. Brayer and J. P. Domonte Tetrahedron Lett. 1996 37 3857. 98 M. Moreno-Man8 as M. Pe� rez and R. Pleixats J. Org. Chem. 1996 61 2346. 99 A. B. Charette and A. Giroux J. Org. Chem. 1996 61 8718. 100 I. E. Marko� F. Murphy and S. Dolan Tetrahedron Lett.1996 37 2507. 101 T. R. Hoye and M. Chen J. Org. Chem. 1996 61 7940. 102 J. Wang and A. I. Scott Tetrahedron Lett. 1996 37 3247. 103 S.-K. Kang H.-W. Lee J.-S. Kim and S.-C. Choi Tetrahedron Lett. 1996 37 3723. 104 S. Yoshida H. Kubo T. Saika and S. Katsumura Chem. Lett. 1996 139. 105 T. R. Kelly and F. Lang J. Org. Chem. 1996 61 4623. 106 R. Wu J. S. Schumm D. L. Pearson and J. M. Tour J. Org. Chem. 1996 61 6906. 107 Y. Wei Y. Yang and J.-M. Yeh Chem. Mater. 1996 8 2659. 108 G. Langli L.-L. Gundersen and F. Rise Tetrahedron 1996 52 5625. 109 A. I. Meyers and K. A. Novachek Tetrahedron Lett. 1996 37 1747. 110 P. Bernabe� F. P. J. T. Rutjes H. Hiemstra and W. N. Speckamp Tetrahedron Lett. 1996 37 3561. 111 W. D. Schmitz and D. Romo Tetrahedron Lett. 1996 37 4857. 112 C.Subramanyam S. Chattarjee and J. P. Mallamo Tetrahedron Lett. 1996 37 459. 113 D. A. P. Delnoye R. P. Sijbesma J. A. J. M. Vekemans and E. W. Meijer J.Am. Chem. Soc. 1996 118 8717. 114 G. B. Bates and D. Parker Tetrahedron Lett. 1996 37 267. 115 K. C. Nicolaou M. Sato N. D. Miller J. L. Gunzner J. Renaud and E. Untersteller Angew. Chem. Int. Ed. Engl. 1996 35 889. 116 J. S. Xiang A. Mahadevan and P. L. Fuchs J. Am. Chem. Soc. 1996 118 4284. 117 F. Lhermitte and B. Carboni Synlett 1996 377. 118 A.M. Castan8 o and A. M. Echavarren Tetrahedron Lett. 1996 37 6587. 119 G. A. Kraus and B. M. Watson Tetrahedron Lett. 1996 37 5287. 120 G. Macdonald N. J. Lewis and R. J. K. Taylor Chem. Commun. 1996 2647. 121 R. J. Boyce and G. Pattenden Tetrahedron Lett. 1996 37 3501. 122 T. Yokomatsu T.Yamagishi K. Matsumoto and S. Shibuya Tetrahedron Lett. 1996 37 11 725. 123 M. D. Matteucci and U. von Krosigk Tetrahedron Lett. 1996 37 5057. 124 T. S. McDermott A. A. Mortlock and C. H. Heathcock J. Org. Chem. 1996 61 700. 125 S. Marquais and M. Arlt Tetrahedron Lett. 1996 37 5491. 126 A. Weichert M. Bauer and P. Wirsig Synlett 1996 473. 127 L. Villar J. P. Bullock M. M. Khan A. Nagarajan R.W. Bates S. G. Bott G. Zepeda F. Delgado and J. Tamariz J. Organomet. Chem. 1996 517 9. 128 C. Malan and C. Morin Synlett 1996 167. 129 G.-Q. Shi X.-H. Huang and F. Hong J. Org. Chem. 1996 61 3200. 130 S. Superchi N. Sotomayor G. Miao B. Joseph and V. Snieckus Tetrahedron Lett. 1996 37 37 6057. 131 I. Klement M. Rottla� nder C. E. Tucker T. N. Majid P. Knochel P. Venegas and G. Cahiez Tetrahedron 1996 52 7201.132 P. A. Evans and T. A. Brandt Tetrahedron Lett. 1996 37 1367. 133 M. Rottla� nder N. Palmer and P. Knochel Synlett 1996 573. 134 M. Amat S. Hadida and J. Bosch An. Quim. 1996 92 62. 135 T. Sakamoto Y. Kondo N. Takazawa and H. Yamanaka J. Chem. Soc. Perkin Trans. 1 1996 1927. 136 B. A. Anderson and N. K. Harn Synthesis 1996 583. 137 I. Mangalagiu T. Benneche and K. Undheim Tetrahedron Lett. 1996 37 1309. 138 X. Huang and L. S. Zhu Synthesis 1996 1191. 139 L.-L. Gundersen Acta Chim. Scand. 1996 50 58. 140 J. P. Wolfe and S. L. Buchwald J. Org. Chem. 1996 61 1133. 141 M. S. Driver and J. F. Hartwig J. Am. Chem. Soc. 1996 118 7217. 238 G.R. Stephenson 142 J. P. Wolfe S. Wagaw and S. L. Buchwald J. Am. Chem. Soc. 1996 118 7215. 143 S.-H. Zhao A. K. Miller J.Berger and L. A. Flippin Tetrahedron Lett. 1996 37 4463. 144 J. P. Wolfe R. A. Rennels and S. L. Buchwald Tetrahedron 1996 52 7525. 145 S. Wagaw and S. L. Buchwald J. Org. Chem. 1996 61 7240. 146 S. R. Gilbertson and G. W. Starkey J. Org. Chem. 1996 61 2922. 147 M. Mladenova M. Alami and G. Linstrumelle Tetrahedron Lett. 1996 37 6547. 148 V. Fiandanese G. Marchese A. Punzi and G. Ruggieri Tetrahedron Lett. 1996 37 8455. 149 M. Vlassa I. Ciocan-Tarta F. Margineanu and I. Oprean Tetrahedron 1996 52 1337. 150 X. Huang and Y.-P. Wang Synth. Commun. 1996 26 3087. 151 W. A. Herrmann C.-P. Reisinger K. Ofele C. Brosmer N. Beller and H. Fischer J. Mol. Catal. A; 1996 105 51. 152 M. Pal and N. G. Kundu J. Chem. Soc. Perkin Trans. 1 1996 449. 153 N. A. Bunagin L. J. Sukhomlmova E. V. Luzihova T.P. Tolstaya and I. P. Beletskava Tetrahedron Lett. 1996 37 897. 154 S.-K. Lee H.-W. Lee S.-B. Jang and P. S. Ho Chem. Commun. 1996 835. 155 S. F. Vasilevsky and T. A. Prikhod’ko Mendeleev Commun. 1996 98. 156 N. A. Powell and S. D. Rychnovsky Tetrahedron Lett. 1996 37 7901. 157 X.-S. Ye and H. N. C. Wong Chem. Commun. 1996 339. 158 A. G. Mal’kina L. Brandsma S. F. Vasilevsky and B. A. Trofimov Synthesis 1996 589. 159 A. Arcadi O. A. Attanasi L. de Crescentini E. Rossi and F. Serra-Zanetti Tetrahedron 1996 52 3997. 160 M. A. Ciufolini J. W. Mitchell and F. Roschangar Tetrahedron Lett. 1996 37 8281. 161 M. Abarbri J.-L. Parrain J.-C. Cintrat and A. Duche� ne Synthesis 1996 82. 162 J. H. Ryan and P. J. Stang J. Org. Chem. 1996 61 6162. 163 A. I. Meyers and K. A. Novachek Tetrahedron Lett.1996 37 1747. 164 J. Uenishi R. Kawahama and O. Yonemitsu J. Org. Chem. 1996 61 5716. 165 C.-J. Li D. Wang and W. T. Slaven IV Tetrahedron Lett. 1996 37 4459. 166 N. G. Kundu J. S. Mahanty and C. P. Spears Bioorg. Med. Chem. Lett. 1996 6 1497. 167 P. Das and N. G. Kundu J. Chem. Res. (S). 1996 298. 168 F. Seela and M. Zulauf Synthesis 1996 726. 169 M. Alami F. Ferri and Y. Gaslain Tetrahedron Lett. 1996 37 57. 170 S. Chackalamannil R. J. Davies T. Asberom D. Doller and D. Leone J. Am. Chem. Soc. 1996 118 9812. 171 M. Eckhardt and R. Bru� ckner Angew. Chem. Int. Ed. Engl. 1996 35 1093. 172 O. Lavastre L. Ollivier P. H. Dixneuf and S. Sibaudhit Tetrahedron 1996 52 5495. 173 F. Zeng and S. C. Zimmerman J. Am. Chem. Soc. 1996 118 5326. 174 A. Goeke M. Sawamura R. Kuwano and Y.Ito Angew. Chem. Int. Ed. Engl. 1996 35 662. 175 H. Jiang S. Ma G. Zhu and X. Lu Tetrahedron 1996 52 10 945. 176 J. Ji Z. Wang and X. Lu Organometallics 1996 15 2821. 177 D. L. Boger C. M. Tarby P. L. Myers and L. H. Caporale J. Am. Chem. Soc. 1996 118 2109. 178 B. M. Trost and Y. Li J. Am. Chem. Soc. 1996 118 6625. 179 H. Yamada S. Aoyagli and G. Kibayashi J. Am. Chem. Soc. 1996 118 1054. 180 M. Toyota Y. Nishikawa and K. Fukumoto Tetrahedron 1996 52 10 347. 181 M. Toyota T. Asoh and K. Fukumoto Tetrahedron Lett. 1996 37 4401. 182 B. M. Trost F. J. Fleitz and W.J. Watkins J. Am. Chem. Soc. 1996 118 5164. 183 T. Ohshima K. Kagechika M. Adachi M. Sodeoka and M. Shibasaki J. Am. Chem. Soc. 1996 118 7108. 184 S. P. Maddaford N. G. Andersen W.A. Cristofoli and B. A. Keay J. Am. Chem. Soc.1996 118 10 766. 18 J. M. Sansano D. Wilson and J. Redpath Tetrahedron Lett. 1996 37 4413. 186 R. Grigg V. Sridharan and C. Terrier Tetrahedron Lett. 1996 37 4221. 187 T. Doi A. Yanagisawa S. Nakanishi K. Yamamoto and T. Takahashi J. Org. Chem. 1996 61 2602. 188 T. Doi A. Yanagisawa T. Takahashi and K. Yamamoto Synlett 1996 145. 189 J.-F. Nguefack V. Bolitt and D. Sinou Tetrahedron Lett. 1996 37 59. 190 A. Ali G. B. Gill G. Pattenden G. A. Roan and T.-S. Kam J. Chem. Soc. Perkin Trans. 1 1996 1081. 191 R. Grigg and J. M. Sansano Tetrahedron 1996 52 13 441. 192 R. Grigg and L.-H. Xu Tetrahedron Lett. 1996 37 4251. 193 H. Henniges F. E. Meyer U. Schick F. Funke A. De Meijere and P. J. Parsons Tetrahedron 1996 52 11 545. 194 R. Grigg V. Loganathan V. Sridharan P.Stevenson S. Sukirthalingam and T. Worakun Tetrahedron 1996 52 11 479. 195 M. Davicchioli D. Bouyssi J. Gore� and G. Balme Tetrahedron Lett. 1996 37 1429. 196 M. Cavicchioli S. Decortiat D. Bouyssi J. Gore� and G. Balme Tetrahedron 1996 52 11 463. 197 R. Grigg and V. Savic Tetrahedron Lett. 1996 37 6565. 198 J.-F. Nguefack V. Bolitt and D. Sinou Tetrahedron Lett. 1996 37 5527. 199 R. Grigg R. Rasul J. Redpath and D. Wilson Tetrahedron Lett. 1996 37 4609. 200 V. Gauthier B. Cazes and J. Gore� Bull. Soc. Chim. Fr. 1996 133 563. 201 K. Nozaki N. Sato and H. Takaya Bull. Chem. Soc. Jpn. 1996 69 1629. 239 Organometallic chemistry the transition metals 202 M. Botta V. Summa F. Corelli G. Di Pietro and P. Lombardi Tetrahedron Asymmetry 1996 7 1263. 203 A. Arcadi S. Cacchi M. Del Rosario G.Fabrizi and F. Marinelli J. Org. Chem. 1996 61 9280. 204 R. Grigg V. Loganathan and V. Sridharan Tetrahedron Lett. 1996 37 3399. 205 C. H. Oh C. Y. Rhim J. H. Kang A. Kim B. S. Park and Y. Seo Tetrahedron Lett. 1996 37 8875. 206 S. Saito M. M. Salter Y. Gevorgyan N. Tsuboya K. Tando and Y. Yamamoto J. Am. Chem. Soc. 1996 118 3970. 207 J. Krause K.-J. Haack K. R. Po� rschke B. Gabor R. Goddard C. Plunta and K. Seevogel J. Am. Chem. Soc. 1996 118 804. 208 H. Corlay A. M.Z. Slawin D. J. Williams W. B. Motherwell A.M. K. Pennell M. Shipman P. Binger and M. Stopp Tetrahedron 1996 52 4883. 209 R. C. Larock and E. K. Yum Tetrahedron 1996 52 2743. 210 H. Corlay E. Fouquet and W.B. Motherwell Tetrahedron Lett. 1996 37 5983. 211 F. A. Khan R. Czerwonka and H.-U. Reissig Synlett 1996 533.212 M. Lautens and Y. Ren J. Am. Chem. Soc. 1996 118 9597. 213 R. C. Larock and F. K. Yum Tetrahedron 1996 52 2743. 214 K. H. Ang S. Brase A. G. Steinig F. E. Meyer A. Llebaria K. Boigt and A. De Meijere Tetrahedron 1996 52 11 503. 215 J. S. Koh and J. A. Ellman J. Org. Chem. 1996 61 4494. 216 C. Cope� ret S. Ma T. Sugihara and E.-I. Negishi Tetrahedron 1996 52 11 529. 217 E.-I. Negishi C. Cope� ret S. Ma T. Mita T. Sugihara and J. M. Tour J. Am. Chem. Soc. 1996 118 5904. 218 E. Negishi S. Ma J. Amanfu C. Cope� ret J. A. Miller and J. M. Tour J. Am. Chem. Soc. 1996 118 5919. 219 B. E. Ali K. Okuro G. Vasapollo and H. Alper J. Am. Chem. Soc. 1996 118 4264. 220 R. Grigg B. Putnikovic and C. J. Urch Tetrahedron Lett. 1996 37 695. 221 M. Sperrle and G. Consiglio J. Organomet. Chem.1996 506 177. 222 H. Pellissier S. Wilmouth and M. Stantelli Tetrahedron Lett. 1996 37 5107. 223 K. Krisnudu P. R. Krishna and H. B. Mereyala Tetrahedron Lett. 1996 37 6007. 224 P. Campain J. Gore� and J.-M. Vate` le Tetrahedron 1996 52 10 405. 225 Y. I. M. Nilsson R. G. P. Gatti P. G. Andersson and J.-E. Ba� ckvall Tetrahedron 1996 52 7511. 226 Y. I. M. Nilsson A. Aranyos P. G. Andersson J.-E. Ba� ckvall J.-L. Parrain C. Ploteau and J.-P. Quintard J. Org. Chem. 1996 61 1825. 227 K. J. Szabo� J. Am. Chem. Soc. 1996 118 7818. 228 E. Monflier S. Tilloy E. Blouet Y. Barbaux and A. Montreux J. Mol. Catal. A. 1996 109 27. 229 M. P. Doyle C. S. Peterson and D. L. Parker Jnr. Angew. Chem. Int. Ed. Engl. 1996 35 1334. 230 N. Watanabe H. Matsuda H. Kuribayashi and S. Hashimoto Heterocycles 1996 42 537.231 H.M. L. Davies P. R. Bruzinski D. H. Lake N. Kong and M.J. Fall J. Am. Chem. Soc. 1996 118 6897. 232 M. P. Doyle Q. L. Zhou C. Charnsangavej M. A. Longoria M. A. McKervey and C. F. Garcia Tetrahedron Lett. 1996 37 4129. 233 H.M. L. Davies P. R. Bruzinski and M. J. Fall Tetrahedron Lett. 1996 37 4133. 234 R. T. Buck M. P. Doyle M.J. Drysdale L. Ferris D. C. Forbes D. Haigh C. J. Moody N. D. Pearson and Q.-L. Zhou Tetrahedron Lett. 1996 37 7631. 235 L. Ferris D. Haigh and C. J. Moody Tetrahedron Lett. 1996 37 107. 236 H.M. L. Davies and B. D. Doan Tetrahedron Lett. 1996 37 3967. 237 A. G. H. Wee and B. Liu Tetrahedron Lett. 1996 37 145. 238 H.W. L. Davies G. Ahmed and M.R. Churchill J. Am. Chem. Soc. 1996 118 10 774. 239 D. F. Taber K. K. You and A. L. Rheingold J.Am. Chem. Soc. 1996 118 547. 240 A. G. H. Wee and J. Slobodian J. Org. Chem. 1996 61 2897. 241 A. F. Mateos G. P. Coca J. J. P. Alonso R. R. Gonza� lez C. T. Herna� ndez Synlett 1996 1134. 242 D. F. Taber and Y. Song J. Org. Chem. 1996 61 7508. 243 D. F. Taber R. J. Herr S. K. Pack and J. M. Geremia J. Org. Chem. 1996 61 2908. 244 E. Aller R. T. Buck M. J. Drysdale L. Ferris D. Haigh C. J. Moody N. D. Pearson and J. B. Sanghera J. Chem. Soc. Perkin Trans. 1 1996 2879. 245 S. N. Osipov N. Sewald A. F. Kolomiets A. V. Fokin and K. Burger Tetrahedron Lett. 1996 37 615. 246 C. J. Moody and M.C. Bagley Synlett 1996 1171. 247 J.-P. Barnier and L. Blanco J. Organomet. Chem. 1996 514 67. 248 K. Smith and D. Bahzad J. Chem. Soc. Perkin Trans. 1 1996 279. 249 K. E. Brighty and M. J. Castaldi Synlett 1996 1097.250 M. P. Doyle and A. V. Kalinin J. Org. Chem. 1996 61 2179. 251 T. A. Chappie R. M. Weekly and M.C. McMills Tetrahedron Lett. 1996 37 6523. 252 M. P. Doyle M.N. Protopopova C. S. Peterson and J. P. Vitale J. Am. Chem. Soc. 1996 118 7865. 253 P. Mu� ller C. Baud and Y. Jacquier Tetrahedron 1996 52 1543. 254 M. C. Pirrung and Y. R. Lee Tetrahedron Lett. 1996 37 2391. 255 H.M. L. Davies J. J. Matasi and G. Ahmed J. Org. Chem. 1996 61 2305. 256 A. Oku S. Ohki T. Yoshida and K. Kimura Chem. Commun. 1996 1077. 257 A. Padwa D. J. Austin and S. F. Hornbuckle J. Org. Chem. 1996 61 63. 240 G.R. Stephenson 258 M. Prein and A. Padwa Tetrahedron Lett. 1996 37 6981. 259 A. Pawda A. T. Price and L. Zhi J. Org. Chem. 1996 61 2283. 260 R. Navarro E. P. Urriolabeitia C.Cativiela M. D. Diaz-de-Villegas M. P. Lo� pez and E. Alonso J. Mol. Catal. A 1996 105 111. 261 J. J. Eisch Y. Qian and M. Singh J. Organomet. Chem. 1996 512 207. 262 V. K. Aggarwal H. Abdel-Rahman L. Fan R. V. H. Jones and M. C. H. Standen Chem. Eur. J. 1996 2 1024. 263 O. Fujimura and R. H. Grubbs J. Am. Chem. Soc. 1996 118 2499. 264 S. F. Martin H.-J. Chen A. K. Courtney Y. Liao P. M. Yusheng M. Pa� tzel M. N.Ramser and A. S. Wagman Tetrahedron 1996 52 7251. 265 M. S. Visser N. M. Heron M. T. Didiuk J. F. Sagal and A. H. Hoveyda J. Am. Chem. Soc. 1996 118 4291. 266 S. K. Armstrong and B. A. Christie Tetrahedron Lett. 1996 37 9373. 267 H. S. Overkleeft and U. K. Pandit Tetrahedron Lett. 1996 37 547. 268 J. D. Winkler J. E. Stelmach and J. Axten Tetrahedron Lett. 1996 37 4317. 269 A.Fu� rstner and N. Kindler Tetrahedron Lett. 1996 37 7005. 270 A. Fu� rstner and K. Langemann J. Org. Chem. 1996 61 3942. 271 S. J. Miller H. E. Blackwell and R. H. Grubbs J. Am. Chem. Soc. 1996 118 9606. 272 M. T. Crimmins and B. W. King J. Org. Chem. 1996 61 4192. 273 A. G. M. Barrett S. P. D. Baugh V. C. Gibson M.R. Giles E. L. Marshall and P. A. Procopiou Chem. Commun. 1996 2231. 274 W. J. Zuercher M. Hashimoto and R. H. Grubbs J. Am. Chem. Soc. 1996 118 6634. 275 J. S. Clark and J. G. Kettle Tetrahedron Lett. 1997 38 123. 276 B. Ko� nig and C. Horn Synlett 1996 1013. 277 M. A. McKervey and M. Pitarch Chem. Commun. 1996 1689. 278 F. Garro-He� lion and F. Guibe� Chem. Commun. 1996 641. 279 D.M. Walba P. Keller R. Shao N. A. Clark M. Hillmyer and R. H. Grubbs J. Am. Chem. Soc. 1996 118 2740.280 M. F. Schneider and S. Blechert Angew. Chem. Int. Ed. Engl. 1996 35 411. 281 J. H. van Maarseveen J. A. J. den Hartog V. Engelen E. Finner G. Vissev and C. G. Krase Tetrahedron Lett. 1996 37 8249. 282 A. Kinoshita and M. Mori J. Org. Chem. 1996 61 8356. 283 D. F. Harv268. 284 S.-H. Kim W. J. Zuercher N. B. Bowden and R. H. Grubbs J. Org. Chem. 1996 61 1073. 285 F. J. Schattenmann R. R. Schrock and W.M. Davis J. Am. Chem. Soc. 1996 118 3295. 286 T. Luker and R. J. Whitby Tetrahedron Lett. 1996 37 7661. 287 T. Takahashi R. Hara Y. Nishihara and M. Kotora J. Am. Chem. Soc. 1996 118 5154. 288 K. Miura M. Funatsu H. Saito H. Ito and A. Hosomi Tetrahedron Lett. 1996 37 9059. 289 P. Wipf and W. Xu J. Org. Chem. 1996 61 6556. 290 L.Hermans and S. F. Mapolie Polyhedron 1997 16 869. 291 F. R. Alam K. A. Azam S. E. Kabir and S. S. Ullah Indian J. Chem. Sect. A 1996 35 317. 292 S. J. Shieh T. C. Tang J.-S. Lee G. H. Lee S.-M. Peng and R.-S. Liu J. Org. Chem. 1996 61 3245. 293 B. Rudolf and J. Zakrewski J. Organomet. Chem. 1996 522 313. 294 Z.-W. Guo and A. Zamojski Tetrahedron 1996 52 12 553. 295 K. Wis� niewski Z. Pakulski A. Zamojski and W.S. Sheldrick J. Organomet. Chem. 1996 523 1. 296 J. M. Cooney L. Main and B. K. Nicholson J. Organomet. Chem. 1996 516 191. 297 J. M. Cooney C. V. Depree L. Main and B. K. Nicholson J. Organomet. Chem. 1996 515 109. 298 G. R. Clark M.R. Metzler G. Whitaker and P. D. Woodgate J. Organomet. Chem. 1996 513 109. 299 J. L. Kiplinger and T. G. Richmond Polyhedron 1997 16 409. 300 S.Legoupy C. Cre� visy J.-C. Guillemin and R. Gre� e Tetrahedron Lett. 1996 37 1225. 301 C. Carfagna N. Carr R. J. Deeth S. J. Dossett M. Green M.F. Mahon and C. Vaughan J. Chem. Soc. Dalton Trans. 1996 415. 302 D. Enders S. von Berg and B. Jandeleit Synlett 1996 18. 303 D. Enders P. Fey T. Schmitz B. B. Lohray and B. Jandeleit J. Organomet. Chem. 1996 514 227. 304 D. Enders U. Frank P. Fey B. Jandeleit and B. B. Lohray J. Organomet. Chem. 1996 519 147. 305 S. Nakanishi H. Yamaguchi K. Okamoto and T. Takata Tetrahedron Asymmetry 1996 7 2219. 306 C.-C. Chen J.-S. Fan S.-J. Shieh G.-H. Lee S.-M. Peng S.-L. Wang and R.-S. Liu J.Am. Chem. Soc. 1996 118 9279. 307 J. E. Muir A. Haynes and A. Winter Chem. Commun. 1996 1765. 308 H.-J. Kno� lker and W. Fro� hner Tetrahedron Lett. 1996 37 9183.309 H.-J. Kno� lker G. Baum and J.-B. Pannek Tetrahedron 1996 52 7345. 310 H.-J. Kno� lker F. Budei J.-B. Pannek G. Schlechtingen Synlett 1996 587. 311 C.W. Ong H. M. Wang and Y. A. Chang J. Org. Chem. 1996 61 3996. 312 E. J. Sandoe G. R. Stephenson and S. Swanson Tetrahedron Lett. 1996 37 6283. 313 A. F. H. Siu L. A. P. Kane-Maguire S. G. Pyne and R. M. Lambrecht J. Chem. Res. (S) 1996 395. 241 Organometallic chemistry the transition metals 314 M. Ka¡§ ser and A. Salzer J. Organomet. Chem. 1996 508 219. 315 U. Englert B. Ganter M. Ka¡§ ser E. Klinkhammer T. Wagner and A. Salzer Chem. Eur. J. 1996 2 523. 316 R. D. A. Hudson S. A. Osborne and G. R. Stephenson Synlett 1996 845. 317 J. A. S. Howell A. G. Bell P. J. O¡�Leary G. R. Stephenson M. Hastings P.W. Howard D. A. Owen A.J. Whitehead P. McArdle and D. Cunningham Organometallics 1996 15 4247. 318 S.-S. P. Chou and C.-H. Hsu J. Chin. Chem. Soc. (Taipei) 1996 43 355. 319 S.-S. P. Chou and C.-H. Hsu Tetrahedron Lett. 1996 37 5373. 320 R. D. A. Hudson S. A. Osborne E. Roberts and G. R. Stephenson Tetrahedron Lett. 1996 37 9009. 321 C. Guillou N. Millot V. Reboul and C. Thal Tetrahedron Lett. 1996 37 4515. 322 A. Hirschfelder D. Drost S. Meinhardt and P. Eilbracht Chem. Ber. 1996 129 845. 323 A. Braun L. J. Toupet and J.-P. Lellouche J. Org. Chem. 1996 61 1914. 324 C. J. M. Kermarrec J. T. Martelli D. M. Gre¢¥ e J.-P. Lellouche and L. J.Toupet J. Org. Chem. 1996 61 1918. 325 T. J. Benvegnu L. J. Toupet and R. L. Gre¢¥ e Tetrahedron 1996 52 11 811. 326 V. Prahlad and W.A. Donaldson Tetrahedron Lett. 1996 37 9169.327 I. Ripoche K. Bennis J.-L. Canet J. Gelas and Y. Troin Tetrahedron Lett. 1996 37 3991. 328 W. A. Donaldson and L. Shang Tetrahedron Lett. 1996 37 423. 329 S. Nakanishi K. Kumeta Y. Sawai and T. Takata J. Organomet. Chem. 1996 515 99. 330 N. J. Marchand D. M. Gre¢¥ e J.T. Martelli R. L. Gre¢¥ e and L. J. Toupet J. Org. Chem. 1996 61 5063. 331 Y. Takemoto J. Takeuchi E. Matsui and C. Iwata Chem. Pharm. Bull. 1996 44 948. 332 M. Franck-Neumann L. Miesch-Gross and O. Nass Tetrahedron Lett. 1996 37 8763. 333 W. R. Roush and A. B. Works Tetrahedron Lett. 1996 37 8065. 334 A. Boha¢¥ c¢§ A.M. Lettrichova¢¥ P. Hrnc¢§iar and M. Hutta J. Organomet. Chem. 1996 507 23. 335 W. Adam and R. M. Schuhmann Liebigs Ann. 1996 635. 336 C.W. Ong and T.-L. Chien Organometallics 1996 15 1323.337 W. Adam and R. M. Schuhmann J. Org. Chem. 1996 61 874. 338 M. R. Attwood T. M. Raynham D. G. Smyth and G. R. Stephenson Tetrahedron Lett. 1996 37 2731. 339 T. A. Petrel J. M. Stephan K. F. McDaniel M. C. McMills A. L. Rheingold and G. P. A. Yap J. Org. Chem. 1996 61 4188. 340 M. G. Banwell and H.M. Schuhbauer Organometallics 1996 15 4078. 341 J. A. Tallarico M. L. Randall and M.L. Snapper J. Am. Chem. Soc. 1996 118 9196. 342 S. V. Ley and G. Meek Chem. Commun. 1996 317. 343 S. V. Ley and L. R. Cox Chem. Commun. 1996 657. 344 J. Bo¡§ hmer W. Fo¡§ rtsch F. Hampel and R. Schobert Chem. Ber. 1996 129 427. 345 M.-L. Lai S.-C. Chang C.-C. Hwu and M.-C. P. Yeh Tetrahedron Lett. 1996 37 6149. 346 M.-C. P. Yeh L.-W. Chuang and C.-H. Ueng J. Org. Chem. 1996 61 3874. 347 W. Blankenfeldt J.-W.Liao L.-C. Lo and M.-C. P. Yeh Tetrahedron Lett. 1996 37 7361. 348 A. Hirschfelder and P. Eilbracht Synthesis 1996 488. 349 G. Tewes A. Hirschfelder and P. Eilbracht Tetrahedron 1996 52 5449. 350 M. M. Schulze and U. Gockel Tetrahedron Lett. 1996 37 357. 351 F. Maywald and P. Eilbracht Synlett 1996 380. 352 H.-J. Kno¡§ lker and H. Hermann Angew. Chem. Int. Ed. Engl. 1996 35 341. 353 C.W. Ong C. S. Huang and T. H. Chang Organometallics 1996 15 4334. 354 R. S. Paley M. B. Rubio R. F. de la Pradilla R. Dorado G. Hundal (ne¢¥ e Sood) and M. Mart©¥¢¥ nez-Ripoll Organometallics 1996 15 4672. 355 H.-J. Kno¡§ lker P. Gonser and T. Ko¡§ gler Tetrahedron Lett. 1996 37 2405. 356 M. Franck-Neumann P. Sto¡§ ber and (in part) G. Passmore Tetrahedron Asymmetry 1996 7 3193. 357 J. A. S. Howell P.J. O¡�Leary M.G. Palin G. Jaouen and S. Top Tetrahedron Asymmetry 1996 7 307. 358 Y. Takemoto Y. Baba I. Noguchi and C. Iwata Tetrahedron Lett. 1996 37 3345. 359 R. Bru¡§ nner and H. Gerlach Tetrahedron Asymmetry 1996 7 1515. 360 A. L. Rheingold B. S. Haggerty H. Ma and R. D. Ernst Acta Crystallogr. Sect. C. 1996 52 1110. 361 M. F. N. N. Carvalho A. J. L. Pombeiro I. M. Shropshire and G. R. Stephenson Inorg. Chim. Acta 1996 248 45. 362 S. A. Benyunes and S. E. Gibson (ne¢¥ e Thomas) Chem. Commun. 1996 43. 363 S. A. Benyunes S. E. Gibson (ne¢¥ e Thomas) and M. A. Peplow Chem. Commun. 1996 1757. 364 K.-C. Shih and R. J. Angelici J. Org. Chem. 1996 61 7784. 365 M. J. Ackland T. N. Danks and M. E. Howells Tetrahedron Lett. 1996 37 691. 366 H.-J. Kno¡§ lker H. Goesmann and P. Gonser Tetrahedron Lett.1996 37 6543. 367 H. Cherkaoui J. T. Martelli and R. L. Gre¢¥ e J. Organomet. Chem. 1996 522 311. 368 S. E. Gibson (ne¢¥ e Thomas) M.F. Ward M. Kipps P. D. Stanley and P. A. Worthington Chem. Commun. 1996 263. 369 H.-J. Kno¡§ lker H. Goesmann and C. Hofmann Synlett 1996 737. 370 H.-J. Kno¡§ lker and C. Hofmann Tetrahedron Lett. 1996 37 7947. 371 M.-C. P. Yeh and C.-N. Chaung J. Chem. Soc. Perkin Trans. 1 1996 2167. 242 G.R. Stephenson 372 S.-S. P. Chou and H.-T. Sheng Organometallics 1996 15 4113. 373 C. Slugovc K. Mauthner K. Mereiter R. Schmid and K. Kirchner Organometallics 1996 15 2954. 374 C. Butters N. Carr R. J. Deeth M. Green S. M. Green and M.F. Mahon J. Chem. Soc. Dalton Trans. 1996 2299. 375 Y. D. Ward L. A. Villaneuva G. D. Allred and L. S. Liebeskind J.Am. Chem. Soc. 1996 118 897. 376 L. Besson M. Le Bail D. J. Aitken H.-P. Husson F. Rose-Munch and E. Rose Tetrahedron Lett. 1996 37 3307. 377 D. Beruben and E. P. Ku� ndig Helv. Chim. Acta 1996 79 1533. 378 D. Amurrio K. Khan and E. P. Ku� ndig J. Org. Chem. 1996 61 2258. 379 K. Kamikawa and M. U. 1996 37 6359. 380 F.-E. Hong S.-C. Lo M.-W. Liou L.-F. Chou and C.-C. Lin J. Organomet. Chem. 1996 516 123. 381 M. F. Semmelhack and H.-G. Schmalz Tetrahedron Lett. 1996 37 3089. 382 A. J. Pearson A. V. Gontcharov and P. D. Woodgate Tetrahedron Lett. 1996 37 3087. 383 S. Qiao D. A. Hoic and G. C. Fu J. Am. Chem. Soc. 1996 118 6329. 384 W. Chen J. B. Sheridan M. L. Cote� and R. A. Lalancette Organometallics 1996 15 2700. 385 E. J. Corey and C. J. Helal Tetrahedron Lett.1996 37 4837. 386 A. Bassoli L. Merlini C. Baldoli S. Maiorana and M.G. B. Drew Tetrahedron Asymmetry 1996 7 1903. 387 C. Kermarrec V. Madiot D. M. Gre� e A. Meyer and R. L. Gre� e Tetrahedron Lett. 1996 37 5691. 388 M. J. Siwek and J. R. Green Synlett 1996 560. 389 V. A. Mal’tseva and D. V. Mironov Russ. J. Coord. Chem. (Transl. of Koord. Khim.) 1996 22 664. 390 S. Goetgheluck J. Lamiot and J. Brocard J. Organomet. Chem. 1996 519 87. 391 R. A. Ewin and N. S. Simpkins Synlett 1996 317. 392 E. L. M. Cowton S. E. Gibson (ne� e Thomas) M. J. Schneider and M. H. Smith Chem. Commun. 1996 839. 393 S. E. Gibson (ne� e Thomas) P. C. V. Potter and M. H. Smith Chem. Commun. 1996 2757. 394 M. J. Siwek and J. R. Green Chem. Commun. 1996 2359. 395 J. A. S. Howell M. G. Palin G. Jaouen B.Malezieux S. Top J. M. Cense J. Salau� n P. McArdle D. Cunningham and M. O’Gara Tetrahedron Asymmetry 1996 7 95. 396 J.-F. Carpentier L. Pamart L. Maciewjeski Y. Castanet J. Brocard and A. Mortreux Tetrahedron Lett. 1996 37 167. 397 K. Kamikawa T. Watanabe and M. Uemura J. Org. Chem. 1996 61 1375. 398 R. F. W. Jackson D. Turner and M. H. Block Synlett 1996 862. 399 S. G. Davies and L. M. A. R. B. Correia Chem. Commun. 1996 1803. 400 N. Taniguchi N. Kaneta and M. Uemura J. Org. Chem. 1996 61 6088. 401 C. Mukai S. Hirai I. J. Kim and M. Hanaoka Tetrahedron Lett. 1996 37 5389. 402 J. G. Rodrý� guez A. Urrutia I. Fonseca and J. Sanz J. Organomet. Chem. 1996 522 231. 403 C. Baldoli P. Del Buttero E. Licandro A. Papagni and T. Pilati Tetrahedron Lett. 1996 37 4849. 404 C. Baldoli P.Del. Buttero M. Di Ciolo S. Maiorana and A. Papagni Synlett 1996 258. 405 E. P. Ku� ndig L. H. Xu P. Romanens and G. Bernardinelli Synlett 1996 270. 406 S. E.Gibson (ne� e Thomas) R. Gil F. Prechtl A. J. P. White and D. J. Williams J. Chem. Soc. Perkin Trans. 1 1996 1007. 407 S. Sur S. Ganesh D. Pal V. G. Puranik P. Chakrabarti and A. Sarkar J. Org. Chem. 1996 61 8362. 408 H.-G. Schmalz S. Siegel and A. Schwarz Tetrahedron Lett. 1996 37 2947. 409 M. Brands H. G. Wey J. Bruckmann C. Krueger and H. Butenschoen Chem. Eur. J. 1996 2 182. 410 L. A. Paquette T. M. Morwick J. T. Negri and R. D. Rogers Tetrahedron 1996 52 3075. 411 E. P. Ku� ndig J. Leresche L. Saudan and G. Bernardinelli Tetrahedron 1996 52 7363. 412 J. H. Rigby and P. Sugathapala Tetrahedron Lett. 1996 37 5293. 413 J. H.Rigby S. D. Rege V. P. Sandanayaka and M. Kirova J. Org. Chem. 1996 61 842. 414 J. H. Rigby V. de Sainte Claire S. V. Cuisiat and M. J. Heeg J. Org. Chem. 1996 61 7992. 415 J. H. Rigby N. C. Warshakoon and M. J. Heeg J. Am. Chem. Soc. 1996 118 6094. 416 J. H. Rigby and N. C. Warshakoon J. Org. Chem. 1996 61 7644. 417 J. H. Rigby and F. C. Pigge Synlett 1996 631. 418 W. Chen K. Cha§ee H.-J. Chung and J. B. Sheridan J. Am. Chem. Soc. 1996 118 9980. 419 W. Chen H.-J. Chung C. Wang J. B. Sheridan M.L. Cote� and R. A. Lalancette Organometallics 1996 15 3337. 420 F. Balssa V. Gagliardini F. Rose-Munch and E. Rose Organometallics 1996 15 4373. 421 V. Gagliardini F. Balssa F. Rose-Munch E. Rose C. Susanne and Y. Dromzee J. Organomet. Chem. 1996 519 281. 422 F. Rose-Munch C. Susanne C. Renard E.Rose and J. Vaisserman J. Organomet. Chem. 1996 519 253. 423 J. Chen V. G. Young Jr. and R. J. Angelici Organometallics 1996 15 325. 424 C. A. Dullaghan S. H. Sun G. B. Carpenter B. Weldon and D. A. Sweigart Angew. Chem. Int. Ed. Engl. 1996 35 212. 425 S. H. Sun G. B. Carpenter and D. A. Sweigart J. Organomet. Chem. 1996 512 257. 426 S. Lee S. R. Lovelace D. J. Arford S. J. Geib S. G. Weber and N. J. Cooper J. Am. Chem. Soc. 1996 118 4190. 243 Organometallic chemistry the transition metals 427 Y. Yu J. Chen X. Wang Q. Wu and Q. Liu J. Organomet. Chem. 1996 516 81. 428 H.-J. Chung J. B. Sheridan M. L. Cote� and R. A. Lalancette Organometallics 1996 15 4575. 429 A. J. Pearson P. Zhang and K. Lee J. Org. Chem. 1996 61 6581. 430 A. J. Pearson and G. Bignan Tetrahedron Lett.1996 37 735. 431 R. C. Cambie G. R. Clark S. L. Coombe S. A. Coulson P. S. Rutledge and P. D. Woodgate J. Organomet. Chem. 1996 507 1. 432 A. A. Dembek and P. J. Fagan Organometallics 1996 15 1319. 433 A. J. Pearson A. M. Gelormini M. A. Fox and D. Watkins J. Org. Chem. 1996 61 1297. 434 P. C. B. Gomes E. J. S. Vichi P. J. S. Moran A. F. Neto M.L. Maroso and J. Miller Organometallics 1996 15 3198. 435 P. Magnus R. Carter M. Davies J. Elliott and T. Pitterna Tetrahedron 1996 52 6283. 436 K. Mikami F. Feng H. Matsueda A. Yoshida and D. S. Grierson Synlett 1996 833. 437 G. B. Jones R. S. Huber J. E. Mathews and A. Li Tetrahedron Lett. 1996 37 3643. 438 D. Vourloumis K. D. Kim J. L. Petersen and P. A. Magriotis J. Org. Chem. 1996 61 4848. 439 S.-I. Hashimoto Y. Miyazki and S. Ikegami Synlett 1996 324.440 T. Nagasawa K. Taya M. Kitamura and K. Suzuki J. Am. Chem. Soc. 1996 118 8949. 441 S. Dare B. Ducroix S. Bernard and K. M. Nicholas Tetrahedron Lett. 1996 37 4341. 442 C. Mukai and M. Hanaoka Synlett 1996 11. 443 J. Bach R. Bergenuer J. Garcia T. Loscertales and J. Vilarrasa J. Org. Chem. 1996 61 9021. 444 M. E. Kra§t Y. Y. Cheung C. Wright and R. Cali J. Org. Chem. 1996 61 3912. 445 J. G. Donkervoort A. R. Gordon C. Johnstone W.J. Kerr and U. Lange Tetrahedron 1996 52 7391. 446 J. Castro A. Moyano M. A. Perica` s A. Riera A. E. Green A. Alvarez-Larena and J. F. Piniella J. Org. Chem. 1996 61 9016. 447 J. Marco-Contelles J. Org. Chem. 1996 61 7666. 448 W. J. Kerr G. G. Kirk and K. Middlemiss J. Organomet. Chem. 1996 519 93. 449 J. C. Anderson B. F. Taylor C. Viney and G.J. Wilson J. Organomet. Chem. 1996 519 103. 450 G. L. Bolton Tetrahedron Lett. 1996 37 3433. 451 B. L. Pagenkopf and T. Livinghouse J. Am. Chem. Soc. 1996 118 2285. 452 M. L. N. Rao and M. Periasamy Organometallics 1996 15 442. 453 J. Tormo X. Verdaguer A. Moyano M.A. Perica` s and A. Riera Tetrahedron 1996 52 14 021. 454 S. G. Van Ornum and J. M. Cook Tetrahedron Lett. 1996 37 7185. 455 M. Thommen A. L. Veretenov R. Guidetii-Grept and R. Keese Helv. Chim. Acta 1996 79 461. 456 M. E. Kra§t A. M. Wilson O. A. Dasse B. Shao Y. Y. Cheung Z. Fu L. V. R. Bonaga and M.K. Mollman J. Am. Chem. Soc. 1996 118 6080. 457 J. K. Cammack S. Jalisatgi A. J. Matzger A. Negro� n and K. P. C. Vollhardt J. Org. Chem. 1996 61 4798. 458 D. Llerena C. Aubert and M. Malacria Tetrahedron Lett. 1996 37 7027.459 D. Llerena C. Aubert and M. Malacria Tetrahedron Lett. 1996 37 7353. 460 W. Tully L. Main and B. K. Nicholson J. Organomet. Chem. 1996 507 103. 461 J. Bao W.D. Wul§ M. J. Fumo E. B. Grant D. P. Heller M. C. Whitcomb and S.-M. Yeung J. Am. Chem. Soc. 1996 118 2166. 462 J. Bao W. D. Wul§ J. B. Dominy M.J. Fumo E. B. Grant A. C. Rob M. C. Whitcomb S.-M. Yeung R. L. Ostrander and A. L. Rheingold J. Am. Chem. Soc. 1996 118 3392. 463 J. P. A. Harrity N. M. Heron W.J. Kerr S. McKendry K. Middlemiss and J. S. Scott Synlett 1996 1184. 464 R. P. Hsung W.D. Wul§ and C. A. Challener Synthesis 1996 773. 465 O. Kretschik M. Nieger and K. H. Do� tz Organometallics 1996 15 3625. 466 T. Leese and K. H. Do� tz Chem. Ber. 1996 129 623. 467 A. Rahm and W. D. Wul§ J. Am. Chem. Soc. 1996 118 1807.468 M. E. Bos W.D. Wul§ and K. J. Wilson Chem. Commun. 1996 1863. 469 J. T. Lin J. J. Wu C.-S. Li Y. S. Wen and K.-J. Lin Organometallics 1996 15 5028. 470 F. Coat and C. Lapinte Organometallics 1996 15 477. 471 M. I. Bruce M. Ke and P. J. Low Chem. Commun. 1996 2405. 472 Y. Hayashi M. Osawa K. Kobayashi and Y. Wakatsuki Chem. Commun. 1996 1617. 473 J. D. Bradshaw L. Guo C. A. Tessier and W. J. Youngs Organometallics 1996 15 2582. 474 G. Jia H. P. Xia W.F. Wu and W. S. Ng Organometallics 1996 15 3634. 47s and R. Ho§mann J. Am. Chem. Soc. 1996 118 10 294. 476 B. Bildstein H. Kopacka M. Schweiger E. Ellmerer-Mu� ller K.-H. Ongania and K. Wurst Organometallics 1996 15 4398. 477 S. Guesmi D. Touchard and P. H. Dixneuf Chem. Commun. 1996 2773. 478 E.Viola C. Lo Sterzo and F. Trezzi Organometallics 1996 15 4352. 479 S. T. Mabrouk and M.D. Rausch J. Organomet. Chem. 1996 523 111. 480 R.-Z. Jin S.-S. Xu X.-Z. Zhou R.-J. Wang and H.-G. Wang Gaodeng Xeuxiao Huaxue Xuebao 1996 17 722 (Chem. Abstr. 1996 125 86787w). 481 C. P. Casey C. J. Czerwinski and R. K. Hayashi Organometallics 1996 15 4362. 482 E. Louattani J. Suades A. Alvarez-Larena J. F. Piniella and G. Germain J. Organomet. Chem. 1996 506 244 G.R. Stephenson 121. 483 J.-F. Capon N. Le Bere-Cosquer B. Leblanc and R. Kergoat J. Organomet. Chem. 1996 58 31. 484 J.-F. Capon N. Le Berre-Cosquer and R. Kergoat J. Organomet. Chem. 1996 508 1. 485 S. L. Ingham B. F. G. Johnson F. G. Brian K. J. Taylor and L. J. Yellowlees J. Chem. Soc. Dalton Trans. 1996 3521. 486 M. H. A.Benvenutti P. B. Hitchcock J. F. Nixon and M. D. Vargas J. Chem. Soc. Dalton Trans. 1996 739. 487 W.-Y. Wong and W.-T. Wong J. Chem. Soc. Dalton Trans. 1996 3209. 488 S. S. Lee T.-Y. Lee J. E. Lee I.-S. Lee and Y. K. Chung Organometallics 1996 15 3664. 489 M. Sato A. Kudo Y. Kawata and H. Saitoh Chem. Commun. 1996 25. 490 M. Sato Y. Hayashi S. Kumakura N. Shimizu M. Katada and S. Kawata Organometallics 1996 15 721. 491 M. Sato and E. Mogi J. Organomet. Chem. 1996 517 1. 492 H. Fischer F. Leroux G. Roth and R. Stampf Organometallics 1996 15 3723. 493 U. H. Bunz and J. E. C. Wiegelmann-Kreiter Chem. Ber. 1996 129 785. 494 G. Cooke and O. Schulz Synth. Commun. 1996 26 2549. 495 E. Stankovic¡ P. Elec¡ko and S¢. Toma Chem. Pap. 1996 50 68. 496 U. Behrens H. Brussard V. Hagenau J. Heck E.Hendrickx J. Ko� rnich J. G.M. van der Linden A. Persoons A. L. Spek M. Veldman B. Voss and H. Wang Chem. Eur. J. 1996 2 98. 497 I. R. Whittall M. G. Humphrey A. Persoons and S. Houbrechts Organometallics 1996 15 1935. 498 A.M. McDonagh I. R. Whittall M. G. Humphrey B.W. Skelton and A. H. White J. Organomet. Chem. 1996 519 229. 499 G. Iftime J.-C. Daran E. Menoury and G. G. A. Balavoine Organometallics 1996 15 480. 500 V. Alain A. Fort M. Barzoukas C.-T. Chen M. Blachard-Desce S. R. Marder and J. W. Perry Inorg. Chim. Acta 1996 242 43. 501 R. Herrmann G. Wagner and C. Zollfrank Electron. Conf. Trends Org. Chem. (ECTOC 1) (CD-ROM) Royal Society of Chemistry Cambridge 1996 paper 49 (Chem. Abstr. 1996 125 11 053v). 502 P. G. Lacroix S. Di Bella and I. Ledoux Chem. Mater. 1996 8 541.503 S. Guha W.T. Roberts and B. H. Ahn Appl. Phys. Lett. 1996 68 3686. 504 W. Wenseleers E. Goovaerts A. S. Dhindsa and A. E. Underhill Chem. Phys. Lett. 1996 254 410. 505 S. Shi Z. Lin Y. Mo X. Q. Xin J. Phys. Chem. 1996 100 10 696. 506 T. Kamata H. Kambayashi S. Kubota T. Fukaya H. Matsuda F. Mizukami and T. Uchida Mol. Cryst. Liq. Cryst. Sci. Technol. Sect. B 1996 15 255. 507 F. Ja� kle K. Polborn and M. Wagner Chem. Ber. 1996 129 603. 508 T. Moriuchi I. Ikeda and T. Hirao J. Organomet. Chem. 1996 514 153. 509 F. L. Atkinson N. C.Brown N. G. Connelly A. G. Orpen A. L. Reiger P. H. Reiger and G.M. Rosair J. Chem. Soc. Dalton Trans. 1996 1959. 510 R.W. Lass P. Steinert J. Wolf and H. Werner Chem. Eur. J. 1996 2 19. 511 F. Hojo K. Fukiki and W. Ando Organometallics 1996 15 3606. 512 M.Tamm A. Grzegorzewski and I. Bru� dgam J. Organomet. Chem. 1996 519 217. 513 M. Tamm A. Grzegorzewski T. Steiner T. Jentzsch and W. Werncke Organometallics 1996 15 4984. 514 M. S. Morton J. P. Selegue and A.Carrillo Organometallics 1996 15 4664. 515 T. J. J. Mu� ller and H. G. Lindner Chem. Ber. 1996 129 607. 516 R. Boese G. Braunlich J.-P. Gotteland J.-T. Hwang C. Troll and K. P. C. Vollhardt Angew. Chem. Int. Ed. Engl. 1996 35 995. 517 C. Vale� rio B. Gloaguen J.-L. Fillaut and D. Astruc Bull. Soc. Chim. Fr. 1996 133 101. 518 H.-W. Marx F. Moulines T. Wagner and D. Astruc Angew. Chem. Int. Ed. Engl. 1996 35 1701. 519 M. J. Begley P. Mountford P. J. Steward D. Swallow and S. Wan J. Chem. Soc. Dalton Trans. 1996 1323. 520 C. Bonifaci G. Carta A. Ceccon S. Gambaro S. Santi and A.Venzo Organometallics 1996 15 1630. 521 E. S. Davies and M.W. Whiteley J. Organomet. Chem. 1996 519 261. 522 D. S. Brown M.-H. Delville K. P. C. Vollhardt and D. Astruc Organometallics 1996 15 2360. 523 P. S. McGovern and K. P. C. Vollhardt Chem. Commun. 1996 1593. 524 I. Kova� cs and M. C. Baird Organometallics 1996 15 3588. 525 C. T. Qian J. H. Guo and J. Sun Chin. Chem. Lett. 1996 7 189. 526 R. Deschenaux M. Schweissguth and A.-M. Levelut Chem. Commun. 1996 1275. 527 K. Wang S. Mun8 oz L. Zhang R. Castro A. E. Kaifer and G. W. Gokel J. Am. Chem. Soc. 1996 118 6707. 528 A. S. Abd-El-Aziz C. R. de Denus K. M. Epp S. Smith R. J. Jaeger and D. T. Pierce Can. J. Chem. 1996 74 650. 529 Z. Liu Y. Sun and Y. Shang Huaxue Shiji 1996 18 5 (Chem. Abstr. 1996 125 86805a). 530 Y.-H. Liu Y.-J.Wu H.-Y. Yun L. Yang and Q.-X. Xiu Gaodeng Xuexiao Huaxue Xuebao 1996 17 1225 (Chem. Abstr. 1996 125 276 101r). 531 R. S. Herrick R. M. Jarret T. P. Curran D. R. Dragoli M.B. Flaherty S. E. Lindyberg R. A. Slate and L. C. Thornton Tetrahedron Lett. 1996 37 5289. 532 G. Wagner R. Herrmann and W. Scherer J. Organomet. Chem. 1996 516 225. 533 C. Zhang and K. Yang Gaodeng Xuexiao Huaxue Xuebao 1996 17 401 (Chem. Abstr. 1996 125 58668q). 245 Organometallic chemistry the transition metals 534 D. Huang J. Yang W. Wan F. Ding L. Zhang Y. Liu and S. Xiang Mol. Cryst. Liq. Cryst. Sci. Technol. Sect. A 1996 281 43. 535 J. Yang D. Huang F. Ding K. Zhao W. Guan and L. Zhang Mol. Cryst. Liq. Cryst. Sci. Technol. Sect. A 1996 281 51. 536 E. Campillos R. Deschenaux A.-M. Levelut and R. Ziessel J.Chem. Soc. Dalton Trans. 1996 2533. 537 Y.-H. Liao and J. R. Moss Organometallics 1996 15 4307. 538 I. Cuadrado M. Mora� n C.M. Casado B. Alonso F. Lobete B. Garcý� a M. Ibisate and J. Losada Organometallics 1996 15 5278. 539 Y. Ni R. Rulkens and I. Manners J. Am. Chem. Soc. 1996 118 4102. 540 D. L. Zechel K. C. Hultzsch R. Rulkens D. Balaishis Y. Ni J. K. Pudelski A. J. Lough and I. Manners Organometallics 1996 15 1972. 541 R. Rulkens R. Lough and A. J. Manners Angew. Chem. Int. Ed. Engl. 1996 35 1805. 542 R. Rulkens A. J. Lough I. Manners S. R. Lovelace C. Grant and W. E. Geiger J. Am. Chem. Soc. 1996 118 12 683. 543 O. Lavastre M. Even P. H. Dixneuf A. Pacreau and J.-P. Vairon Organometallics 1996 15 1530. 544 R. D. Markwell I. S. Butler A. K. Kakkar M.S. Khan Z. H. Al-Zakwani and J.Lewis Organometallics 1996 15 2331. 545 S. Setayesh and U. H. F. Bunz Organometallics 1996 15 5470. 546 M. Altmann V. Enkelmann and U. H. F. Bunz Chem. Ber. 1996 129 269. 547 S. S. H. Mao and T. D. Tilley J. Organomet. Chem. 1996 52 425. 548 M. J. Irwin J. J. Vittal G. P. A. Yap and R. J. Puddephatt J. Am. Chem. Soc. 1996 118 13 101. 549 F. Li H. Zhang L. Chen Q. Wu H. Xue and H. Zhang Synth. React. Inorg. Metal-Org. Chem. 1996 26 339. 550 P. J. Davies N. Veldman D. M. Grove A. L. Spek B. T. G. Lutz and G. van Koten Angew. Chem. Int. Ed. Engl. 1996 35 1959. 551 D. P. Dygutsch and P. Eilbracht Tetrahedron 1996 15 5461. 552 R. Deschenaux V. Izvolenski F. Turpin D. Guillon and B. Heinrich Chem. Commun. 1996 439. 553 S. R. Gilbertson X. Wang G. S. Hoge C. A. Klug and J. Schaefer Organometallics 1996 15 4678.554 V. Isaeva A. Derouault and J. Barrault Bull. Soc. Chim. Fr. 1996 133 351. 555 E. Ho� fer E. Steckhan B. Ramos W. R. Heineman J. Electroanal. Chem. 1996 402 115. 556 P. D. Beer A. R. Graydon and L. R. Sutton Polyhedron 1996 15 2457. 557 Z. Chem. A. R. Graydon and P. D. Beer J. Chem. Soc. Faraday Trans. 1996 92 97. 558 N. Komatsuzuaki M. Uno K. Shirai Y. Takai T. Tanaka M. Sawada and S. Takahashi Bull. Chem. Soc. Jpn. 1996 69 17. 559 P. D. Beer and K. Y. Wild Polyhedron 1996 15 775. 560 H. Plenio and D. Burth Organometallics 1996 15 1151. 561 C. E. Anson T. J. Baldwin C. S. Creaser M. A. Fey and G. R. Stephenson Organometallics 1996 15 1451. 562 C. E. Anson C. S. Creaser and G. R. Stephenson Spectrochim. Acta Part A 1996 52 1183. 563 Suo;Hare Organometallics 1996 15 3885. 564 C. D. Hall A. Leineweber J. H. R. Tucker and D. J. Williams J. Organomet. Chem. 1996 523 13. 565 R. A. Bartsch P. Kus R. A. Holwerda B. P. Czech X. Kou and N. K. Dalley J. Organomet. Chem. 1996 522 9. 566 N. Chabert-Couchouron C. Reibel C. Marzin and G. Tarrago An. Quim. Int. Edn. 1996 92 70. 567 N.M. Loin N. V. Abramova and V. I. Sokolov Mendeleev Commun. 1996 46. 568 M. Sawamura Y. Nakayama W.-M. Tang and Y. Ito J. Org. Chem. 1996 61. 9090. 569 S. Top J. Tang A. Vessie` res D. Carrez C. Provot and G. Jaouen Chem. Commun. 1996 955. 570 A. Pio� rko R. G. Sutherland A. Vessie` res-Jaouen and G. Jaouen J. Organomet. Chem. 1996 512 79. 571 F. Wu� st H. Spies and B. Johannsen Bioorg. Med. Chem. Lett. 1996 6 2729. 572 R. K. Hom D. Y. Chi and J.A. Katzenellenbogen J. Org. Chem. 1996 61 2624. 573 Y. Sugano and J. A. Katzenellenbogen Bioorg. Med. Chem. Lett. 1996 6 361. 574 H. Chen S. Ogo and R. H. Fish J. Am. Chem. Soc. 1996 118 4993. 575 S. Blanalt M. Salmain B. Male� zieux and G. Jaouen Tetrahedron Lett. 1996 37 6561. 576 H. El Amouri Y. Besace J. Vaissermann and G. Jaouen J. Organomet. Chem. 1996 515 103. 577 E. N. Korneeva M.V. Ovchinnikov and N. M. Kostic� Inorg. Chim. Acta 1996 243 9. 578 D. A. Pearson J. Lister-James W. J. McBride D.M. Wilson L. J. Martel E. R. Civitello J. E. Taylor B. R. Moyer and R. T. Dean J. Med. Chem. 1996 39 1361. 579 K. L. Cunningham and D. R. McMillin Polyhedron 1996 15 1673. 580 H. Plenio and C. Aberle Chem. Commun. 1996 2123. 581 C. Guillon and P. Vierling J. Organomet. Chem. 1996 506 211.582 R. Sanders and U. T. Mueller-Westerho§ J. Organomet. Chem. 1996 512 219. 583 T.-Y. Dong and L.-L. Lai J. Organomet. Chem. 1996 509 131. 584 J.-G. Rodriguez A. Onate R. M. Martin-Villamil and I. Fonseca J. Organomet. Chem. 1996 513 71. 585 G. Iftme C. Moreau-Bossuet E. Manoury and G. A. Balavone Chem. Commun. 1996 527. 586 T. Sammakia and H. A. Latham J. Org. Chem. 1996 61 1629. 246 G.R. Stephenson 587 K. H. Ahn C.-W. Cho H.-H. Baek J. Park and S. Lee J. Org. Chem. 1996 61 4937. 588 J. Park S. Lee K. H. Ahn and C.-W. Cho Tetrahedron Lett. 1996 37 6137. 589 M. Tsukazaki M. Tinkl A. Roglans B. J. Chapell N. J. Taylor and V. Snieckus J. Am. Chem. Soc. 1996 118 685. 590 Y. Nishibayashi Y. Arikawa K. Ohe and S. Uemara J. Org. Chem. 1996 61 1172. 591 D. Enders R. Lochtman and G.Raabe Synlett 1996 126. 592 L. Schwink and P. Kno� chel Tetrahedron Lett. 1996 37 25. 593 W. Henderson A. G. Oliver and A. J. Downard Polyhedron 1996 15 1165. 594 J.-T. Wang X. Feng L.-F. Tang and Y.-M. Li Polyhedron 1996 15 2997. 595 A. J. Locke and C. J. Richards Tetrahedron Lett. 1996 37 7861. 596 B. Jedlicka R. E. Ru� lke W. Weissensteiner R. Ferna� ndez-Gala� n F.A. Jalo� n B.R. Manzano J. Rodrý�guez-de la Fuente N. Veldman H. Kooijman and A. L. Spek J. Organomet. Chem. 1996 516 97. 597 Y. Nishibayashi K. Segawa J. D. Singh S. Fukazawa K. Ohe and S. Uemura Organometallics 1996 15 370. 598 Y. Nishibayashi K. Segawa H. Takada K. Ohe and S. Uemura Chem. Commun. 1996 847. 599 W. Zhang T. Kida Y. Nakatsuji and I. Ikeda Tetrahedron Lett. 1996 37 7995. 600 B. F. M. Kimmich C.R. Landis and D. R. Powell Organometallics 1996 15 4141. 601 P. E. M. Siegbahn J. Am. Chem. Soc. 1996 118 1487. 602 V.M. Mamaev I. P. Gloriozov V. V. Simonyan A. V. Prisyajnyuk and Y. A. Ustyuyk Mendeleev Commun. 1996 146. 603 F. J. Safarowic and J. B. Keister Organometallics 1996 15 3310. 604 J. Belli and C. M. Jensen Organometallics 1996 15 1532. 605 D. B. Grotjahn and H. C. Lo J. Am. Chem. Soc. 1996 118 2097. 606 D. Heller H. Buschmann and H.-D. Scharf Angew. Chem. Int. Ed. Engl. 1996 35 1852. 607 E. T. Singewald X. Shi C. A. Mirkin S. J. Schofer and C. L. Stern Organometallics 1996 15 3062. 608 M. Ballhorn M. G. Partridge R. N. Perutz and M. K. Whittlesey Chem. Commun. 1996 961. 609 C. J. Sleigh S. B. Duckett and B. A. Messerle Chem. Commun. 1996 2395. 610 T. Lian S. E. Bromberg H.Yang G. Proulx R. G. Bergman and C. B. Harris J. Am. Chem. Soc. 1996 118 3769. 611 C. P. Casey W.T. Boese R. S. Carino and P. C. Ford Organometallics 1996 15 2189. 612 G.M. Drienzo P. S. White and M. Brookhart J. Am. Chem. Soc. 1996 118 6225. 613 K. Nakatani M. Wakabayashi K. Chikama and N. Kiramura J. Phys. Chem. 1996 100 6749. 614 D. L. Hughes J. F. Payack D. Cai T. R. Verhoeven and P. J. Reider Organometallics 1996 15 663. 615 F. Squizani E. Stein and E. J. S. Vichi J. Braz. Chem. Soc. 1996 7 127. 616 K. I. Szabo� Organometallics 1996 15 1128. 617 S. Camanyes F. Maseras M. Moreno A. Lledo� s J.M. Lluck and J. Berbra� n J. Am. Chem. Soc. 1996 118 4617. 618 F. Maseras and A. Lledo� s Organometallics 1996 15 1218. 619 K. Wisniewski Z. Pakulski A. Zamojski and W.S. Sheldrick J.Organomet. Chem. 1996 523 1. 620 R. H. Herber E. Bauminger and I. Felner J. Chem. Phys. 1996 104 7. 621 M.-J. Arce A. L. Viado S. I. Khan and Y. Rubin Organometallics 1996 15 4340. 622 H. Werner R. Wiedemann N. Mahr P. Steinert and J. Wolf Chem. Eur. J. 1996 2 561. 623 P. Belanzoni N. Re M. Rosi A. Sgamellotti and C. Floriani Organometallics 1996 15 4264. 624 J. Grobe D. Le Van F. Immel M. Hegemann B. Krebs and M. La� ge Z. Anorg. Allg. Chem. 1996 622 24. 625 T. Lehotkay K. Wurst P. Jaitner and F. R. Kreissl J. Organomet. Chem. 1996 523 105. 626 E. M. Vogl J. Bruckmann C. Kru� ger and M. W. Haenel J. Organomet. Chem. 1996 520 249. 627 J. El Amouri and Y. Besace Organometallics 1996 15 1514. 628 S. Ito N.Morita and T. Asao J. Org. Chem. 1996 61 5077. 629 W. Tully L. Main and B. K. Nicholson J.Organomet. Chem. 1996 507 103. 630 F. Maseras A. Lledo� s M. Costas and J. M. Poblet Organometallics 1996 15 2947. 631 J. E. McGrady R. Stranger M. Brown and M.A. Bennett Organometallics 1996 15 3109. 632 R. H. Mitchell and Y. Chen Tetrahedron Lett. 1996 37 6665. 633 R. L. Beddoes Z. I. Hussain A. Roberts C. R. Barraclough and M. W. Whiteley J. Chem. Soc. Dalton Trans. 1996 3629. 634 R. Malet M. Moreno-Man8 as T. Parella and R. Pleixats J. Org. Chem. 1996 61 758. 635 K. J. Szabo J. Am. Chem. Soc. 1996 118 7818. 636 D. Braga and F. Grepioni Chem. Commun. 1996 571. 247 Organometall