9 Ti Zr and Hf By S.A. COTTON Felixstowe College Maybush Lane Felixstowe Suffolk lP1 I 7NQ UK 1 Metallocarbohedranes The synthesis of metallocarbohedranes represents the most striking development in the chemistry of Ti Zr and Hf this year. Studies of the dehydrogenation of small hydrocarbons with a plasma of titanium revealed’ a superabundant stable cationic species at 528 amu shown by isotopic labelling to be a Ti8C, cluster. Similar clusters have been reported for Zr Hf and V and other reports have concerned Zr,,C,, Zr 8C29 and Zr,,C, which are believed to have multicage structure^.^,^ A pentagonal dodecahedra] structure has been suggested for the M clusters (Figure 1) consistent with ‘titration’ experiments in which eight ammonia molecules were taken up per cluster molecule indicating that all the titaniums were exposed on the surface of the cluster.This structure can also be viewed in terms of a cube of metal atoms face-capped by six C-C units. Several papers have discussed the bonding in the cluster^;^-^ one indicates a more stable structure (Figure 2) where six C units occupy Figure 1 Figure 2 (Reproduced with permission from J. Chem. Soc. Chrm. Commun. 1992 1779) B. C. Guo. K. P. Kerns and A. W. Castleman. Science. 1992. 255 141 I. B.C. Guo S. Wei J. Purnell S. Buzza and A. W. Castleman Science. 1992 256 515. S. Wei B. C. Guo J. Purnell S. Buzza and A. W. Castleman Science. 1992,256,818;J. Phys. Chem.. 1992. 96 4166. R. W. Grimes and J. D. Gale J. Chem. Soc.. Chrm. Commun. 1992 1222.M-M. Rohmer P. de Vaal and M. Benard J. Am. Chem. Soc. 1992 114 9696. Z. Lin and M.B. Hall J. Am. Chem. SOC.,1992 114 10055. ’ I. Dance J. Chrm. Soc. Chrm. Commun.. 1992 1779. ’ L. Pauling. Proc. Nat. Acad. Sci. U.S.A.. 1992 89. 8175. 107 108 S.A. Cotton the butterflies of a Ti tetracapped tetrahedron. A triplet ground state which may exhibit Jahn-Teller distortion is predicted. Using valence-bond theory however Pauling has predicted a cubic structure with flat faces.' 2 Halides and Halide Complexes Several reports again concern fluoro complexes. (NH,)ZrF is isostr~ctural~ with TlZrF whilst the corresponding hydrate has polymeric chains with ZrF,(H,O) coordination; CsZrF,(H,O) is similar. lo CsSZr,F,,.3H,0 has tetrameric chains' ' whilst Cs6Hf6F,,-4H,0 has individual [HfF6I2- ions in addition to the chains and BaZr,Flo.2H,0 has chains with trigonal dodecahedra1 coordination.' The range of compositions of zirconium and hafnium fluoro complexes has been extended.' BaTiOF has cis-connected TiO,F coordination' whilst several hexachlorozircon- ates have been reported." TiCl complexes with a variety of ligands (alcohols pyridines nitriles thf) and their thermal decomposition has been studied,I6 whilst [{ZrCl,(PBu,),},] reacts with pyridines to give dimeric [{ZrC13(4-R-py),},] (R = H CMe, 1-butylpentyl) with short Zr-Zr distances indicating a single bond.' The pyridine complex oxidatively adds Me,CCN to afford a dimer with bridging nitriles (1). [Zr(NCMe),Cl,][FeCl,] has distorted square antiprismatic coordination ge- ometry in the cation.' Tertiary phosphines react" with [ZrCl,(thf),] either by substitution (2 PMe,) or by nucleophilic ring-opening (3 PCy or PPh,). CMe3 I c1 PMe3 PR3 (2) V.V. Tkachev R.L. Davidovich and L.O. Atovmyan Koord. Khim. 1991 17 1483. lo V.V. Tkachev A.A. Udovenko R. L. Davidovich and L.O. Atovmyan Koord. Khim. 1991 17 1635; V. V. Tkachev R.L. Davidovich and L.O. Atovmyan Koord. Khim. 1992 18 38. I' V. V. Tkachev R. L. Davidovich and L. 0.Atovmyan Koord. Khim. 1992 18,42; A. V. Gerasimenko B.V. Buvetskii V.B. Logvinova and R. L. Davidovich Koord. Khim. 1991 17 1485. Y. Gao J. Guery A. Le Bail and C. Jacoboni J. Solid Stare Chem. 1992 98 11. l3 R. L. Davidovich V. B. Logvinova and L.V. Teplukhina Koord. Khim. 1992 IS 48. l4 M. P. Crosnier and J. L. Fourqeet Eur. J. Solid State Inorg. Chem.. 1992 29 199. L. Buscaglioni and H. Sutcliffe J. Alloys Compounds. 1992 185 67. l6 M. Kohutova and M. Zikmund Transition Met. Chem. 1992,17 186; M. Kohutova A. Valene and M. Zikmund Acfa Fac. Rerum. Nat. Uniue. Cornenianae Chim.. 1991 39 121. (Chem. Abstr. 117 84204). D. M. Hoffmann and S. Lee Inorg. Chem. 1992 31 2675. B.I. Kharisov S.I. Troyanov and S.S. Berdonosov Koord. Khim. 1991 17 1473. l9 T. L. Breen and D. W. Stephan Inorg. Chem. 1992 31 4019. Ti Zr and Hf 109 Interest continues in Zr clusters. Centred isolated zirconium clusters are found in2' Rb,Zr,Cl 8C and Li,Zr,Cl 8H whilst electronic spectra have been recorded and extended Huckel calculations carried out for [Zr,Cl,,Z]"~ (Z = B Be Fe).21 Syntheses and structures have been reported for a number of Zr,X,,(PR,) systems (X = C1 Br; R = Me Et Pr etc.).Bond lengths depend on the position in the cluster as well as upon the halogen.22 3 Aqua Ions and Similar Solvated Species Several studies have appeared in this area.The contact contribution to electronic relaxation of the hexa-aquatitanium(rr1) ion has been assessed by NMR dispersion measurements2 whilst dmf exchange in the corresponding dmf solvate has been shown to occur by an associative route., The solvation structure of titanium(1rr) ions in methanol has been probed by ESR; ENDOR25 and NMR have been used to investigate2 the mechanism of axial and equatorial site exchange in [TiO(dmso)J2+.4 Binary Compounds Interest in simple binary compounds is often inspired by applications in materials science.An ah initio study of bonding in rutile-type compounds has appeared,27 whilst linking TiO with an iron porphyrin leads to a catalyst for the photo-oxidation of hydrocarbons under mild conditions.28 TiO catalyses the photo-oxidation of methylaromatics in the presence of silver sulfate.29 Interest in TIN as a material for wear-resistant coatings particularly in microelectronics has led to the study of its preparation in thin films from amide" and amine3' complexes. Titanium diboride has been prepared by cathodic deposition from melts,32 by laser-induced hydrogen reduction of TiCl,/BCl mixtures,, and by reaction of boron with titanium alk~xides.~~ Mercury intercalation of titanium disulfide has been 5 Other Complexes The structure of Cs,[TiO(C20,),]~2H,0 involves tetranuclear anions with six- coordinate titanium., Various titanium(1v) triflate species have been reported,37 J.Zhang R. P. Ziebarth and J. D. Corbett Inory. Chem. 1992 31 614. '' M. R. Bond and T. Hughbanks Inorg. Chem. 1992 31 5015. 22 F.A. Cotton X. Feng M. Shang and W.A. Wojtczak Anyew. Chem.. Int. Ed. Engl.. 1992 31 1050. 23 1. Bertini C. Luchinat and 2. Xia Inorg Chem.. 1992 31 3152. 24 I. Dellavia. L. Helm and A. E. Merbach. Inorg. Chem. 1992 31 2230. 2s S. Schlick and B. E. Myers Z. Naturforsch. Teil A 1992 47. 702. '' I. Dellavia L. Helm and A. E. Merbach. Inorg. Chem.. 1992 31 4151. '' P.Sorantin and K. Schwarz. Inory. Chrm.. 1992. 31 567. 28 R. Amandelli M. Bregola E. Polo V. Carassiti and A. Maldotti J. Chem. Sot. Chem. Comrnun. 1992 1335. '' E. Baaciocchi G. C. Rosato. C. Roi and G. V. Sebastiani Tetrahedron Lett. 1992 33 5437. ") C. H. Winter P. S. Sheridan T. S. Lewkebandara M. J. Heeg and J. W. Proschia J. Am. Chem.Soc. 1992 114 1095. 31 M. E. Gross and T. Siegrist Inory. Chem 1992 31 4898. 32 H.G. Wendt K. Reuhl. and V. Schwartz. J. Appl. Electrochem. 1992 22. 161. 33 J. Elders and J. D. W. Van Voorst. Appl. Surf. Sci.. 1992 54. 135. 34 Z. Jiang and W. E. Rhine Chem. Muter.. 1992. 4 497. 35 E. W. Ong M. J. McKelvey G. Ouvrard and W. S. Glausinger Chem. Muter.. 1992 4 14. 3h A. Facer. W. Bensch and W. Troemal Inorg. Chim. Actu 1992 193 99.37 H. Moulay el Moustapha and J. L. Pascal J. Fluorine Chem.. 1991. 55 63. 110 S.A. Cotton ~ including [Ti(OTf),] '. Macrocyclic complexes have included a crown ether titanoxane (Figure 3) with the cation3* [(TiCl( 12-cro~n-4)0),]~+ TiCl and TiC1 9C(12) b Figure 3 (Reproduced with permission from J. Chem. Soc. Dalton Trans. 1992 1 117) complexes with a substituted triazacycl~nonane,~~ and the 0x0-bridged [{ LM(acac),)0][C10,] (L = 1,4,7-triaza~yclononane).~~ Schiff-base complexes have attracted attention;,l in particular alkylation of [TiCl,(salen)] gives thermally labile trans-[TiMe,(salen)] which undergoes methyl migration to the Schiff base., These reactions are very solvent-dependent and in thf reductive arylations to afford the titanium(n1) compounds [TiR (thf)(salen)] (R = Ph mes) are observed.Mixed Ti(1v) complexes with dithiocarbamate and methyl salicylate ligands have been reported.43 A most interesting example of trigonal monopyramidal coordination is found in [Ti(N,N)] (N3N = [(Bu'Me,Si)NCH,CH,],N) (4),made by sodium amalgam reduction of the (presumably) trigonal bipyramidal Ti" compound [TiCl(N,N)] .44 The related titanium(rv) complex [TiCl{ N(CH,CH2NSiMe3),}] can be converted into isolable butyls; the sec-butyl cleanly metallates on heating or on reaction with dihydr~gen.~~ Six-coordinate zirconium and hafnium trimethyls (5) have been 38 G. R. Willey J. Palin and N. W. Alcock J. Chem. Soc ,Dalton Trans. 1992 1117. 39 A. Bodner P. Jeske T. Weyhermueller K.Wieghardt. E. Dubler H. Schmalle and B. Nuber Inorg. Chem. 1992 31 3737. 40 P. Jeske K. Wieghardt B. Nuber and J. Weiss Inorg. Chim. Actu 1992 193. 9. 41 A. De Blas R. Bastida and M. J. Fuentes Synth. React. Inorg. Metallo-Org. Chem. 1991 21 1273 42 E. Solar] C. Floriani. A. Chiesi-Villa. and C. Rizzoli J. Chem. Soc. Dalton Trans. 1992 367. 43 S. Bhargava R. Bohra and R.C. Mehrotra Transition Met. Chem. 1991. 16. 622. 44 C.C. Cummins J. Lee R. R. Schrock and W. D. Davis Angew. Chem. Int. Ed. Engl. 1992 31 1501. 45 C. C. Cummins R. R. Schrock. and W. M. Davis Organometallics 1992 I I 1452. Ti,Zr and Hf 111 synthesized and the crystal structure of [Hfh4e3{N(SiMe,CH2PMe2),)] has been determined.46 The structure of [Zr(oep),].2dmso confirms the double-decker structure; the dimethylsulphoxide molecules do not ~oordinate.~' Oxidation of the zirconium and hafnium bis(porphyrin) complexes to the mono and dicationic [M(porph),]"+ (n = 1,2) has attracted at ten ti or^;^^.^^ the electron spins in the diamagnetic dications [Zr(porph),12+ are strongly coupled.Crystallographic data confirm the progressive shortening of the interporphyrin distance with concomitant increase in the n-n interaction in moving from neutral to dicationic zirconium tetraphenylporphyrin complexes. [ZrCl,(oep)] has been ~ynthesized;~~ the two halogens can be replaced by a range of substituents (alkyl aryl alkoxy carborane cyclooctatetraenyl; Figure 4); the structures of the carborane5' 'sandwich' [Zr(oep)(C,B,H )] and the dialk~l~~ [Zr( CH,SiMe3 )*(oep)] were determined.>I' 7 R-H R-H RIM R-Me Figure 4 (Reproduced with permission from J. Am. Chem. Soc. 1992 114 2266) An eight-coordinate zirconium Schiff-base complex with two reactive isocyanate groups forms a co-polymer with p~ly(thf).~l Ethylenedioxydiethylenedinitrilotet- raacetic acid (H,egta) forms complexes [M(egta)] with zirconium and hafnium that are isostructural in the solid state but exhibit significantly different NMR beha~iour.~ 46 M.D. Fryzuk A. Carter and S.J. Rettig. Organometallics. 1992 11 469. 41 J. W. Buchler A. De Cian S. Elschner J. Fischer P. Hammerschmitt and R. Weiss Chem. Ber. 1992 125 107. 48 H-J. Kim D. Whang J. Kim and K. Kim Inorg. Chem.1992 31. 3882. 49 H. Brand and J. Arnold J. Am. Chem. Soc. 1992 114 2266. 50 J. Arnold S.E. Johnson C. B. Knobler and M. F. Hawthorne J. Am. Chem. Sac. 1992 114 3996. 51 W. Tong and R.G. Archer Inarg. Chem.. 1992 31 3332. 52 D. F. Evans G.W. Griffiths C. O'Mahoney D. J. Williams. C Y. Wong and J. D. Woollins J. Chern. Soc. Dalton Trans. 1992. 2475. 112 S. A. Cotton 6 Alkoxides Amides and Related Compounds These continue to be of intere~t~~.~~ because of their use in the synthesis of mixed metal oxides like BaTiO, by sol-gel reactions. Several titanium(rI1) aryloxides have been synthesized and structurally characterized (Figure 5);55an electron-diffraction study trans-[TiC12(tmeda)2] I 2RONa R=Ph R = 3,5-(But)2Ph I I R R R R R R R R M = Na(tmeda)2(thf) [(RO),Ti ] [Li(1 tmedah] 4 L i = tmeda-H Figure 5 (Reproduced with permission from Inory.Chem. 1992 31 4933) of [Ti(NMe,),] has been reported56 and a five-coordinated tertiary phosphine adduct of a titanium aryloxide q2-ketone complex has been structurally ~haracterized.~' 53 J. P. Grammatico and J. M. Porte Lopez J. Muter. Sci Muter. Electron.. 1992 3 82. 54 vide M. Yoshimura S. E. Yoo M. Hayashi and N. Ishiwara Ceram. Truns.. 1990 15 427. 55 R. Minhas R. Duchateau S. Gambarotta and C. Bensirnon Inorq. Chem. 1992 31 4933. s6 A. Haaland K. Rypdal H. V. Volden and R.A. Andersen J. Chem. Soc. Dalton Trans.. 1992 891. 57 J.E. Hill. P.E. Fanwick and I.P. Rothwell Orqanometullics 1992 11 1771. Ti,Zr and Iif Hydrolytic reactions have led to the characterization of clusters such [Zr,Ti,(OPr)l,(OAc),o6] [Ti,O,(OEt)8(methaCrylate)8] [TiI8O,,(OBU),,-(acac),] (Figure 6) and [Zr ,FeO(OC,H,) Jacac),] .Figure 6 (Reproduced with permission from Compt. Rend. Acad. Sci. Series 11 1991 313 1247) Titanium-oxo clusters are also reported6 from the reaction of carboxylic acids with TiCI,; the structure of [Ti,CI,(O,CPh),),] has a Ti,O core. [Zr(OR [R = (CF,),CH)] has been synthesized6 and reacted with [TI(OR,)] to give TI,[Zr(OR ),I; the latter has a molecular structure based on a [Zr(OR ),I octahedron with thallium atoms occupying opposite trigonal faces. Syntheses structures and dynamics of several titanium(1v) binaphtholates have been explored.64 The first homoleptic tellurolates [M(TeSi(SiMe,),}] have been reported6’ whilst the reaction of [TiCl,(tmeda),] with LiN(SiMe,) under nitrogen leads to unexpected dinitrogen complexes including, (6).The replacement by titanium of either one or two boron ring atoms in the preparation of borazine analogues has been reported;67 polyamidoimidonitride clusters of zirconium have also been characterized.68 58 I.Lazziz A. Larbot A. Julbe C. Guizard and U. Cot J. Solid State Chem. 1992 98 393. 59 U. Schubert. E. Arpac W. Glaubitt A. Helmerich and C. Chau. Chem. Marer. 1992 4 291. 60 P. Toledano M. In and C. Sanchez Compt. Rend. Acad. Sci.. Ser. 11 1991 131 1247. 61 R. Schmid H. Ahamdane and A. Mosset Inorg. Chim. Acta 1991 190 237. 62 N. W. Alcock D.A. Brown S. M. Roe and M. G. H. Wallbridge,J. Chem.Soc. Chem.Commun. 1992,846. 63 J.A. Samuels J. F. Zwanziger E. B. Lobkovsky and K. G. Caulton Inorg. Chem. 1992 31 4046. 64 T.J. Boyle D. L. Barnes. J. A. Heppert L Morales F.Takusagawa. and J. W. Connolly Organornetallics 1992 11 1112. 65 V. Christou and J. Arnold J. Am. Chem. Soc. 1992 114 6240. 66 N. Beydoun R. Duchateau and S. Gambarotta J. Chem. Soc. Chem. Commun. 1992 244. 67 H.-J. Koch H. H. Roesky R. Bohra M. Noltemeyer and H.-G. Schmidt .4ngew. Chem. In[. Ed. Engl. 1992 31 598. 68 M. M. B. Hall and P.T. Wolczanski d. .4m. Chem. Soc. 1992 114. 3854. ) 114 S.A. Cotton Me3Si PY PY Me3Si-N.,. I I /Cl ,Ti-N-N-Ti; c1 I I N-SiMe, IiY py 'SiMe 7 Phosphates and Related Systems The structure of titanium(II1) phosphate has been determined.69 Potassium titanyl phosphate (KTP; KTiOPO,) is an important ion-conducting non-linear optical material; the effects of a d.c.electric field on its structure have been e~amined,~' whilst the effect of cation substitution upon its structure and optical properties has been e~plored.~ Zirconium phosphates continue to attract attention for their potential for supra- molecular assembly for example and have been reviewed together with other phosphates and phosphonates.72 Syntheses have been reported for chromia-pillared a-zirconium phosphate,73 sodium zirconium phosphate^,?^ and zirconium phosphate hypophosphites and dimethylphosphinate~.~~ The protonic conductivity of layered zirconium phosphonates with -S03H groups has been e~amined,'~ whilst solid state NMR has been used to extract structural information on oriented zirconium bis(phosponoacetic Intercalates of zirconium phosphates and phosphonates have been re~iewed;~' amine intercalates of r-zirconium phosphate have been studied by 31PNMRe7' A study of zirconium phosphate intercalated by organic bases (e.y.phen bipy) showed that the interlayer distance was not a simple function of the size of the guest molecules; iron (11) complexes formed by the intercalated donors" were also studied. Chiral molecular recognition on intercalation has been investigated8 whilst a halide-viologen complex trapped in a zirconium phosphonate matrix has applications in solar energy storage.82 69 R.Glaum and R. Gruehn Z. Kristallogr. 1992 198 41. 70 M. T. Sebastian H. Klapper and R. J. Bolt J. Appl. Crystaloyr. 1992 25 274. 71 M. L. F. Phillips W. T. A. Harrison. G. D. Stucky E. M. McCarron J. C. Calabrese and T. E. Gier Chem. Mater. 1992 4 222. 72 G. Cao H.-G. Hong. and T.E. Mallouk. Ace. Chem. Res. 1992 25 420. 73 P. Mairles-Torres P. Olivera-Pastor E. Rodriguez-Castellon A. Jiminez-Lopez. and A. A. G. Tomlinson J. Mater. Chem. 1992 1 139. 74 M.K. Dongare P. Singh and P. M. Suryavanshi. Maw. Res. Bull. 1992 27! 637. 75 G. Alberti M. Casciola and R. K. Biswas Inorg. Chim. Acta. 1992 201 207. 76 G. Alberti M. Casciola U. Costantino A. Peraio and E. Montoneri Solid Stare lonics 1992 50 315. 77 D.A. Burwell K. G. Valentine J. H.Timmermans and M. E. Thompson J. Am. Chrm. Soc. 1992. 114 4144. 78 G. Alberti and IJ. Costantino Inclusion Compd. 1991 5. 136. 79 D. J. MacLachlan and K. R. Morgan J. Phys. Chrm. 1992 96 3458. Ro I. Tomita K. Sasaki R. Inoue Y. Morino Y.Hasegawa M. Takeda M. Takahashi and I. Nakai New Dev. Ion. Ex&. Proc. In?. Cot$ Ion Exch. 1991 151 (Chem. Ah. 1992 117 142212). G. Cao. M.E. Garcia. M. Alcala L. F. Burgess and T.E. Mallouk. J. .Am. Chem. Soc. 1992 114 7574. 82 L. A. Vermeulen and M. E. Thompson Nature 1992 358 656. Ti,Zr and Hf 115 8 Titanium Silicates and Related Systems A synthetic route has been describeds3 for incorporating up to eight titanium ions per unit cell into titanium silicate molecular sieve (TS-1); a hydrothermal method is reported for preparing a titanium silicoaluminate oxidation ~atalyst.'~ A mixed-valence lanthanum titanium oxosilicate with a quasi-2D rutile-based structure has been described.9 Organometallic Compounds with Polyhapto Ligands Intense activity in this area means that only a selection of papers can be discussed; a-bonded organometallics have already been mentioned in section 5. New routes have been des~ribed~~.~' to [Ti(arene),]" (n = 0 -1 ). The crystal structures8 of 'titanocene' shows it to be a dimeric fulvalene (7); meanwhile [Ti(C,H,),] has been stabilized as the bis(trimethy1phosphine) add~ct.~' The 15-electron tervalent titanium alkyls [TiR(C,R,),] have been studied;'" they are unwilling to form adducts undergo thermal decomposition to form fulvalene type cornplexe~,~' and and oxidize with PbCI forming Ti" corn pound^.^^ Phot~electron'~ ESR94 spectra have been reported for bis(cyclopentadieny1) titanium(w) halides.Very long metal-metal bonds have been observed for some Ti(w) and Zr(m) dimer~;~~.~~ cleavage of some of these paramagnetic Zr(r11) dimers with nucleophiles has been reported. ESR spectra have been obtained from the triplet state in some titanium(m) dimer~.'~ The catalytic and insertion reactions of the 14-electron [MMe(C,R,),] and + R3 A. Thangaraji and S. Sivasanker. J. Chrm. Soc.. Chem. Conimun. 1992. 123. 84 M. A. Camblor. A. Corma. A. Martinez. and J. Perez-Pariente J. Chem. Soc.. Chrm. Commun..1992. 589. " S. Wang and S-J. Whu J. Am. Chem. Soc.. 1992 114 6920.86 H. Bonnemann and B. Kordll Angew. Chem. Inr. Ed. Engl.. 1992. 31 1490. " D.W. Blackburn. D. Britton. and J. E. Ellis Angew. Chem. Int. Ed. Engl. 1992. 31 1495. "'S. I. Troyanov H. Antropiusova and K. Macg J. Oryanomet. Chem. 1992. 427. 49. " D. W. Stephan Oryanometallics. 1992 11 996. 90 G.A. Luinstra. J. Vogelzang and J. H. Teuben. Organometallics 1992. 11 2273. YI G.A. Luinstra and J. H. Teuben. J. Am. Chem. Soc. 1992. 114 3361. 92 G.A. Luinstra and J. H. Teuben Orgunometallics 1992 11. 1793. 93 T. Vondrak. K. Mach and V. Varga. Oryanometallics 1992 It. 2030. 94 K. Mach and J. B. Raynor J. Chem. Soc. Dalton Trans.. 1992. 683. 9s P. B. Hitchcock. M. F. Lappert G. A. Lawless H. Olivier. and E. J. Ryan J. Chem. Soc.. Chem. Commun..1992 474. M. Benard and M.-M. Rohmer. J. Am. Chem. Soc. 1992 114. 4785. 97 E. Samuel J. F. Harrod D. Gourier Y. Dromzee F. Robert and Y. Jeannin. Inorq. Chrm. 1992.31.3252. 116 S. A. Cotton 16-electron [MMeL(C,R,),] + compounds (M = Ti Zr) have been and the first base-free zirconocene hydride made. ''' ' CPMAS-NMR investigations have been made of ~atalysts''~~' where organozirconium compounds are bound to O3 silica and alumina surfaces. The unusual bimetallic complex [Cp:Hf(Cl)(p-Cl)CaCp:] has been described.' O4 Stereoselective synthesis using metallocene complexes has attracted attenti~n.'~~-'~' Phosphine and [{ ZrCpT(N,),} ,(p-N,)] give complexes that react with alkenes and PH, yielding primary alkylphosphines under very mild conditions.'08 98 M.Bochmann and S.J. Lancaster J. Organomet. Chem. 1992 434 C1. 99 A. D. Horton and A. G. Orpen Oryanometallics 1992. 11 8. I00 J. J. W.Eshuis Y. Y. Tan A. Meetsma J. H. Teuben J. Renkma and G.G. Evens. Organometallics 1992 11 362. '01 X. Yang C.L. Stern and T. J. Marks Angew. Chem. Int. Ed. Engl. 1992 31 1375. C. Sishta R. M. Hathorn and T.J.Marks J. Am. Chem. Soc. 1992 114 1112. F. Quignard C. Lecuyer C. Bougault F. Lefebre A. Choplin D.Olivier and J. M. Basset Inorg. Chem.. 1992 31 928. S. C. Sockwell P.S. Tanner and T.P. Hanusa Organometallics 1992. 11. 2634. A. L. Rheingold N. P. Robinson J. Whelan and B. Bosnich. Organometallics 1992 11 1869. J. Okuda Angew. Chem. Int. Ed. Enyl. 1992 31 47. G. Erker Pure Appl. Chem.. 1992 64 393.108 S. Nielsen-Marsh R.J. Crowte and P.G. Edwards J. Chem. Soc. Chem. Commun.. 1992 699.