8 Ti Zr Hf; V Nb Ta; Cr Mo,W; Mn Tc Re BY J. E. NEWBERY Chemical Laboratories University of London Goldsmiths' College London SE 14 6NW 1 Introduction This seems to be the year of nomenclature change and this chapter according to the new IUPAC recommendation now covers groups 4-7. Regardless of the numbering used the chemistry of the early transition continues to be dominated in quantitative terms by the chemistry of molybdenum although there seems to be increasing attention paid to manganese and technetium. There were few general reviews published this year and one of the more interesting general articles is concerned' with a notation system for metal clusters. This uses the Foppl system of polyhedra classification that dates back to 1912. The subsequent sections deal with the chemistry of the elements group-by-group.Each section starts with general points and the behaviour of simple compounds (oxides halides etc.) before passing on to co-ordination and organometallic species. The classification system followed is based upon the ligand complexity and donor- type rather than oxidation number of the metal. 2 Titanium Zirconium and Hafnium Zirconium bromide has been shown2 to react with ammonia to produce a series of complexes formulated ZrBr4nNH3. At -36°C n can equal 9 12 or 17; at room temperature n = 6 and at 200°C n = 2. This contrasts with the chloride where a reaction occurs to give ZrC13NH2.xNH3. The frequency of the M-halogen vibration as determined by infrared and Raman spectroscopy was used3 to suggest assignments in a series of complexes MX4L MX,L2 and MX,L, where M = Ti or Zr X = C1 or Br and L = pyrazole.The terdentate ligand (l) LiN(SiMe2CH2PRJ2(R = Me Pr' Bu') reacts4 with equimolar proportions of either ZrC1 or HfC1 to give an octahedral complex MC13.N(SiMe2CH2PR2)2. The ligand can potentially take either the fuc-or the mer-orientation. Single-crystal X-ray diffraction analysis indicates that while the hafnium species which occurs in both monoclinic and orthorhombic modifications takes the facial option the zirconium complex has the meridional form. In benzene solution both complexes appear to be of the mer-type and no evidence of fluxional behaviour was found. ' T.-Y. Luh H. N. C. Wong and B. F. G. Johnson Angew. Chem. Int. Ed.Engl. 1985,24 45. E. L. Boyle E. S. Dodsworth D. Nicholls and T. A. Ryan Znorg. Chim. Am 1985,100,281. M.P. Pazos Perez M. E. Garcia Fernandez E. Freijanes and M. Gayoso Anal. mim. 1985,81(B) 7. M.D.Fryzuk A. Carter and A. Westerhaus Znorg. Chem. 1985,24 642. 195 J. E. Newberry A series of phosphine complexes,'MC1 (PMe2.CH2CH,.PMe2), (M = Ti V Cr) has been shown' to be trans-octahedral. The titanium compound was notable for being synthesized in high yield by a 'one-pot' reaction of TiC14 phosphine and magnesium in t.h.f. solution. The chemistry of titanium and vanadium porphyrins has been reviewed,6 but the article is mostly concerned with the vanadium species because of their occurrence in oil shales. Examples of titanium phthalocyanines are also rather sparse and a new synthetic route' may help to increase the range of complexes.Addition of TiC14 phthalodinitrile dissolved in a-chloronaphthalene at 220 "C produces on cooling PcTiCl, where Pc = phthalocyaninato. The chlorides can be substituted to give PcTiX (X = catecholate oxalate or peroxide). The structure of the PcTiCl, as determined by X-ray diffraction is quite similar to octaethylporphyrin metal com- plexes with the metal located above the N4 plane. The final paper to be considered in the non-organometallic section concerns a zirconium cluster compound' Z~,(S)(BU'S),~ (2) that was formed by the reaction between Zr(CH,Ph) and four equivalents of Bu'SH. It contains three modes of thiolate binding in one molecule namely monodentate and bridging in both binary and ternary.styles. The structure ~~,(CL~-~>(CL,-~R)(C,-~R),(SR)~, is notable for the comparatively large Zr-S-Zr angle of the p3-Sligand (91.4'). The main thrust of work in this first group of metals is their organometallic chemistry and this has now' merited a 422 page monograph on zirconium and hafnium species alone. Apart from the obvious concern over synthetic and structural features of these compounds there is extensive comment on their application as catalysts and as specialist reagents in organic chemistry. ' G. S. Girolami G. Wilkinson A. M. R. Galas M. Thornton-Pett and M. B. Hursthouse J. Chem. SOC. Dalton Trans. 1985 1339. R. Guilard and C. Lecomte Coord. Chem. Reu. 1985 65 87. ' V. L. Goedken G.Dessy C. Ercolani V. Fares and L. Gastaldi Znorg. Chem. 1985 24 991. D. Coucouvanis A. Hadjikyriacou and M. G. Kanatzidis J. Chem. Soc. Chem. Commun. 1985 1224. 'Chemistry of organo-zirconium and -hafnium compounds' by D. J. Cardin M. F. Lappert and C. L. Raston Ellis Horwood Chichester 1985. 197 Ti,Zr Hf;V Nb Ta; Cr Mo W; Mn Tc Re Most of the reported papers this year involve q-bonded moieties and it is noticeable that there is a strong trend towards the examination of heterobimetallics. Cp2TiX2 complexes are known to possess anti-cancer activity and there are a number of interesting reports in this field. The synthesis" of such complexes with X = -OC(O)R where R = o-NH2C6H4-or PhCONHCH2- may have significant implications for interactions with amino-acid residues in cancerous cells.For X = C1 the hydrolysis characteristics have been studied" at roughly physiological conditions by using 'H n.m.r. In contrast to the more established platinum(rr) anti-tumour agent ('cisplatin') there is rapid 'ioss of chloride and eventual appearance of free cyclopentadiene. Thermolysis of (Cp),ZrH in the presence of phosphine is known to give Zr"' species such as (Cp),ZrH(PR,) for example. If the analogous reaction is carried out' with (Cp),ZrH(CH2PPh2) then a similar product is obtained but if the thermolys,is is cyried out in the absence of phosphine then a complex formulated as (Cp),ZrCH,PPh is produced. Careful examination of the e.s.r. spectra showed that two products were obtained from the thermolysis in the presence of phosphine.The other complex has been tentatively identified as (CP)~Z~C~H~PR,. A tetrameric species [(c~)~Zr]~ is producedt3 when (Cp),ZrH2 is reduced by elemental phosphorus (or antimony or arsenic). It may have a central (Zr) core and a number of interesting reactions have been reported (Scheme 1). Reagents; i phosphorus reduction; ii Ph,PCI; iii Me3SiC1; iv Me3SnC1 Scheme 1 A thio-cluster molecule (CpTi),( P3-S)6 has been prepared14 by the reaction of hydrogen sulphide and (Cp)2Ti(CO)2. The titanium atoms form a Jahn-Teller- distorted trigonal bipyramid with each triangular face capped by a sulphur. The species has an odd number of electrons and is thus paramagnetic. A similar reaction is not observed with the zirconium analogue perhaps because of the low stability of the (111) oxidation state which is formally required for this cluster.Interesting cage-like anions are formed' when stoicheiometric quantities of (Mo207)(%N), (Cp),TiCl and water are reacted together in dichloromethane solution. The product [(Cp)Ti(Mo5OI8)](&N), has been shown to possess a central plane of eight alternating (Mo 0)atoms. Each molybdenum carries a further 10 C. J. Cardin and A. Roy Znorg. Chim. Acra 1985 107 L33. J. H. Toney and T. J. Marks J. Am. Chem. Soc. 1985 107 947. l2 R. Choukroun and D. Gervais J. Chem. SOC.,Chem. Commun. 1985 224. l3 H. Kopf and T. Klapotke 2.Naturforsch. Teil B 1985 40 447. 14 F. Bottomley G. 0. Egharevba and P. S. White J. Am. Chem. SOC.,1985 107 4353. l5 T.M. Che V. W. Day L. C. Francesconi M. F. Fredrich W. G. Klemperer and W. Shum Inorg. Chem. 1985 24. 4055. 198 J. E. Newberry unique oxygen. There is a single oxygen in the centre of this plane. The fifth molybdenum is located on one side of this plane bound via an oxygen to each molybdenum of the plane. In a similar fashion the titanium is bound on the other side of the plane. They differ in that the titanium then carries a 7-Cp group whereas the molybdenum has a further oxygen. The titanium could also be described as being in an eight-membered ring and it is interesting that both rings show alternation in the M-0 distances. Tungsten forms a similar product. Heterobimetallic species often have interesting electrochemical behaviour which can be exploited in catalytic investigations.Using the ligand Ph2PCH2CH2SH a titanium complex (Cp)2Ti(SCH2CH,PPh2)2 can be prepared.I6 This in turn is able to act as a tetradentate ligand to other metals and complex ions such as [(Cp),Ti( SCH2CH2PPh2),Cu]- can be formed. In solution 31P n.m.r. spectroscopic evidence suggests the presence of two conformers and in the solid state X-ray diffraction work shows near tetrahedral environments for each metal. The central core (Ti-S-Cu-S) is coplanar and the Cu-Ti distance of 3.02A offers some evidence of inter-metallic bonding. Cyclic voltammetry showed only irreversible oxidation steps in acetonitrile solution but a clear reversible reduction peak was found at -0.99V (us. SCE). The Ti-Cu interaction could perhaps be used to postulate why the Ti'"/Ti"' couple deviates from the normal irreversible behaviour.A similar coplanar core (Zr-P-Mo-P) is found17 in (Cp),Zr(p-on cis-PPh,),Mo(CO) that was prepared by the action of (CP),Z~(PP~,)~ Mo(C0)4(NHC,Hlo)2. The Mo-Zr distance across the core is 3.30 A which seems too long for metal-metal effects and the only evidence for such interaction is an upfield shift of the Cp resonances in the 'Hn.m.r. spectrum. A similar tungsten species (Cp),Zr(p-PPh,),W(CO), has also been prepared." Both the X-ray results that show Zr-W of 3.29 8 and the infrared spectrum that shows only a small shift in v(CO) suggests little Zr-W interaction. The 31P n.m.r. resonances however are similar to those of some (W Ir) complexes that certainly do have metal-metal bonds.Me (3) Further styles of heterobimetallic interactions are also common and amongst these is the single carbonyl bridging mode (3) found" in (Cp),ZrMe(p-OC)Mo(CO),(Cp). There is no evidence for any Zr-Mo bonding. This mode of bonding may have some relevance in examining insertion reactions at a single zirconium centre where carbonyl residues are inserted2' into the Zr-C bonds of (Cp),ZrMe2. 16 G. S. White and D. W. Stephan Inorg. Chem. 1985 24 1499. 17 L. Gelrnini L. C. Matassa and D. W. Stephan Inorg. Chem. 1985 24 2585. 18 T. S. Targos R. P. Rosen R. R. Whittle and G. L. Geoffroy Inorg. Chem. 1985 24 1375. 19 B. Longato B. D. Martin J. R. Norton,and 0. P. Anderson Inorg. Chem. 985 24 1389. 20 S. Gambarotta S.Strologo C. Floriani A. Chiesi-Villa and C. Guastini Inorg. Chem. 1985 24 654. 199 Ti Zr Hf; V Nb Ta; Cr Mo W; Mn Tc Re 3 Vanadium Niobium and Tantalum The 51V and l7On.m.r. spectroscopic parameters of a whole series of aqueous peroxovanadates have been reported.21 In general the "V resonance increases on protonation substitution of 002-, and on shifting from a tetrahedral to an octahedral configuration. These alterations have enabled several new species to be detected. The structure of V,( P207)3has been reported.22 The compound was produced by direct action between V205 H3P03 and H3P04. It contains double octahedral clusters of (V,O,) units. Many phosphates are known for their intercalation proper- ties and the effect of a variety of metals ions on VOP04.2H20 has been in~estigated.~~ The interlayer separation decreases as the mole fraction of the cation increases.With sodium ions for example three different phases were identified. Two new ternary chalcogenides have been prepared.24 Both Ta2NiSS and Ta2NiSes have layered structures with octahedral tantalum atoms and tetrahedral nickels. They have edge-sharing polyhedra and are diamagnetic semiconductors. Crystals of the cluster compound Nb61, react rapidly with aqueous ammonia and split into thin lamellae. Unfortunately the products quickly become amorphous and it was not possible to isolate25 the crystalline product Nb618( NH,Me),. Single crystal X-ray analysis confirms the retention of the Nb618 cluster which utilizes only 22-electrons for M-M bonding in the cluster.Coordination Compounds.-These are arranged in order of increasing structural complexity (multi-ligand macrocyclic bridged multi-nuclear etc.). The range of complex chemistry is quite wide for these Group 5 metals and includes vanadyl binding to phospholipid membranes2 and the isolation27 of a blood pigment from the tadpole-like organism Ascidia nigra that has the ability to accumulate selectively vanadium from seawater. The peptide glutathione has been shown2' by I3C and 'H n.m.r. relaxation methods to coordinate to oxovanadium(1v) by the use of two carboxylates with no involvement of the -SH groups. A report2 has been made of the synthesis of a number of vanadium(1v) adduct species formulated VO(Chel),L where (Chel) is a chelating ligand such as dithiocarbamate or dithiophosphate and L is an adduct molecule (quinoline or thiourea).These were investigated by electronic spectroscopy and their hyperfine parameters were determined by e.s.r. The adduct formation seems to be similar but weaker than that found for 6-membered rings. Water-exchange in V(H20)2+ cations has been studied3" over the range 255413 K by 170 n.m.r. spectroscopy. The counter-ion CF3S0, was shown to be non-coor- dinating and the water exchange occurs with an associative interchange mechanism. " A. T. Harrison and 0.W. Howarth J. Chem. Soc. Dalton Trans. 1985 1173. 22 K. K. Palkina S. I. Maksimova N. T. Chibiskova K. Schlesinger and G. Ladwig Z. Anorg. Allg. Chem. 1985 529 89. 23 A.J. Jacobson J. W. Johnson J. F. Brody J. C. Scanlon and J. T. Lewandowski Znorg. Chem. 1985 24 1782. 24 S. A. Sunshine and J. A. Ibers Inorg. Chem. 1985 24 3611. 2s F. Stollmaier and A. Simon Znorg. Chem 1985 24 168. 26 M. Bozsik C. Helm L. Laxhuber and H. Mohwald J. Colloid Interface Sci. 1985 107 514. 27 R. C. Bruening E. M. Oltz J. Furukawa K. Nakanishi and K. Kustin J. Am. Chem. SOC.,1985,107,5298. 28 M. Delfini E. Gaggelli A. Lepri and G. Valensin Znorg. Chim. Acta 1985 107 87. 29 A. Jezierski and B. Jezowska-Trzebiatowska Bull. Pol. Acad. Sci. Chem. 1985 33 85. 30 A. D. Huigi L. Helm and A. E. Merbach Helu. Chim. Acta 1985 68 508. 200 J. E. Newberry Electroreduction of NbCl in methanol was used to prepare31 the methoxide Nb(OMe),.This was examined by 93Nb e.s.r. spectroscopy and the ten-line spectrum obtained was shown to be sensitive to the presence of phosphine. Similar Nb” species have been isolated3’ by reduction of the penta-aryloxide Nb(OAr)5 in the presence of a diphosphine. These are formulated Nb(OAr),(diphos) and have a roughly octahedral alignment about the metal with trans aryloxide groups. The thiolate complexes [VE(SCH2CH2S),]’- where E = 0 or S both take a square-pyramidal structure with the E atom at the apex.33 There are few authenticated structures involving a V=S moiety and this example was formed from the 0x0-species by the action of hexamethyldisilthiane (Me3Si),S. The square-planar environment is not essential for stabilizing M=S moieties and NbS(S,CNEt,) has been shown34 to have a distorted pentagonal bipyramidal structure.The crystal has two inequivalent molecules with Nb=S distances of 2.168 and 2.122 A. The orientation of the ethyl group also differs. Two interesting complexes MCl,(phos) have been rep~rted.~~.~~ The addition of PMePh to VCl,(thf) gave3’ VC13(PMePh2), while TaBr3(PMe2Ph) was pre- pared36 by magnesium reduction of a mixture of phosphine and TaBr,. The vanadium complex was shown to be trigonal bipyramidal with axial phosphines but the tantalum complex is square-planar with the phospines occupying cis positions in the equatorial ring. There are two possible apical positions and each was equally represented in the crystals examined. Examination of the n.m.r. spectra of a range of vanadium fluoride complexes in organic solvents such as MeCN MeNO, or CDC13 has allowed some clarification to be made3’ of the nature of the species involved.Both ”V and 19F shifts were measured and the V-F coupling constants found. The series VOCl,-,F, (x = 0 1 2,3 or 4) and VOF3(N03)- VOF2(N03) and VOF(N03)’ were prepared. Shifts range from +43 p.p.m. for VOCl to -826 p.p.m. for VOF( NO3),. Moving on to mononuclear macrocyclic compounds the cage-like amine (4) forms38a complex ion with vanadium(rv) VL4+. The metal sits at the centre of the cage in a near trigonal prismatic site where two of the six NH groups have been deprotonated. This non-oxo type of complex is quite rare for vanadium( IV). Vanadium phthalocyanine like many similar species has photoconductive and semiconductive properties that make it of potential use in xerographic applications.Reaction between VC13 phthalonitrile and varying amounts of 4-t-butylphthalonitrile allows39 a range of dyes to be produced. This alteration of butyl content produces changes in the solid-state structure from an amorphous to a crystalline phase. 31 M. Melnik and P. Sharrock Can. J. Chem. 1985 63 57. 32 T. W. Coffindaffer I. P. Rothwell K. Folting J. C. Huffman and W. E. Streib J. Chem. SOC.,Chem. Commun. 1985 1519. 33 J. K. Money J. C. Huffman and G. Christou Inorg. Chem. 1985 24 3297. 34 Y. Do and R. H. Holm Znorg. Chim. Acta 1985 104 33. 35 R. L. Bansemer J. C. Huffman and K. G. Caulton Inorg. Chem. 1985 24 3003. 36 N. Hovnanian L.G. Hubert-Pfalzgraf and G. Le Borgne Inorg. Chem. 1985 24 4647. 37 R. C. Hibbert J. Chem. Soc. Chem. Commun. 1985 317. 38 P. Comba L. M. Englehardt J. M. Harrowfield G. A. Lawrance L. L. Martin A. M. Sargeson and A.H. White J. Chem. SOC.,Chem. Commun. 1985 174. 39 K.-Y. Law Znorg. Chem. 1985 24 1778. Ti Zr Hf;V Nb Ta; Cr Mo W; Mn Tc Re + yH3 Some interesting4' interconversions of some vanadium porphyrin species are shown in Scheme 2. Starting from the vanadyl species VO(ttp) a range of complexes VNR(ttp) were prepared by aminolysis. These compounds were found to be resistant to aqueous hydrolysis but the vanadyl starting material is recovered by hydrolysis with ethanoic acid. The 'H n.m.r. spectra were similar to that of the vanadyl porphyrin.ttp = tetratolylporphyrin Reagents i (COCI),; ii RNH2; iii MeCOOH (aq) Scheme 2 The final macrocyclic complex to be considered is the Schiff base vanadyl complex (5). The vanadium was found41 to be displaced by 0.23 A towards the vanadyl oxygen away from the equatorial plane. This is claimed as the first structural determination for an oxovanadium( 11) complex with a pentadentate Schiff base. (5) 40 J. W. Buchler and S. Heifer 2. Naturforsch. Teil B 1985 40 1362. E. C. Alyea T. D. Dee and G. Ferguson J. Cryst. Spectrosc. Res. 1985 15 29. 202 J. E. Newberry The reduction of vanadium(r1r) chloride in t.h.f. by metallic zinc which at first sight would be expected.to give VC12.2(thf) has been known for some time to give a binuclear material [V2(thf)6(~-C1)3]2[zn2cl6].A range of similarly formulated species is now being produced for example4 [V,(thf),( p-Cl),].BPh, [V2(thf)6(p-C1)3].AlC2R2. This latter species proved to be a useful starting material for the production of some interesting phosphine complexes and reacts with methanolic trimethylphosphine to give [V( MeOH)JC12 and [V2(PMe,),(p-Cl),]AlEt,Cl,. Both species were fully characterized by X-ray crystallography. Halide bridging is perhaps the most common type of binuclear bridging found in Group 5 metals. Thus if (NSCl) is reacted with VC14 the dimer [VCI,(NSCI)2]2 is produced.44 In a related45 study the compound VBr,(N3S2) was prepared from the corresponding chloro-species by treatment with Me,SiBr in CH2Br2 at 50 "C.It was studied by infrared and ''V n.m.r. spectroscopy and it was shown by single-crystal X-ray diffraction investigation that both halogen complexes take up a similar structure. There is a 6-membered N-S-N-S-N-$ ring and then two p-halogen bridges to give dimers. These are then associated into chains by coupling V -* N interactions between pairs of dimers. The bromo-complex forms chains that are rotated by about 17" from the position found with the chloro-entity. Thiometallates [MS,]"- are known for a number of transition elements but in Group 5 only vanadium seems to be capable of forming a stable species VS',-. This has been shown* to react easily with FeC1 in acetonitrile to produce anions that have the structure [C12Fe(p-S)2V(pS)2FeC12]3-.It has a near linear Fe-V-Fe backbone ( 172.9") and consists of three edge-sharing tetrahedra.As a postscript to this section on coordination chemistry it might be instructive to consider the question of where are the metal-metal bonded compounds of Group 5? Is the failure to isolate convincing specimens due to inherent lack of stability or is it rather a matter of more attractive alternatives? These questions are posed,47 and answered by the application of standard Hartree-Fock and Fenske-Hall calcula- tions. The basic conclusion seems to be that vanadium does offer the promise of multiple M-M bonds if only the correct conditions are selected. Organometallic Compounds.-A review of C-H bond activation in early transition- metal systems has been published.48 This deals with topics such as a-hydride abstraction benzyne formation and cyclometallations.It is largely concerned with tantalum and makes suggestions of areas of future work. The e.p.r. spectrum of tran~-V(C0),(PMe,)~ has been by doping a sample into a single crystal of the corresponding chromium compound. A B2g ground-state is suggested. Non-cyclopentadienyl organometallic compounds of d4 (Nb' or Ta') ions are usually polymeric so it is of some interest to report" the preparation of 42 F. A. Cotton S. A. Duraj and W. J. Roth Inorg. Chem. 1985 24 913. 43 F. A. Cotton S. A. Duraj L. E. Manzer and W. J. Roth 1.Am. Chem. Soc. 1985 107 3850. 44 G. Beber J. Hanich and K. Dehnicke Z. Nuturforsch. Teil B,1985 40,9. 45 J. Hanich W. Willing U.Miiller and K. Dehnicke 2.Nuturforsch. Teil B,1985 40 1457. 46 D. Youngkyu E. D. Simhon and R. H. Holm Inorg. Chem. 1985,24 4635. 47 F. A. Cotton M. P. Diebold and I. Shim Inorg. Chem. 1985 24 1510. 48 I. P. Rothwell Polyhedron 1985 4 179. 49 J. M. McCall J. R. Morton and K. F. Preston Orgunometallics 1985 4 1272. 50 M. L. Luetkens Jr. D. J. Santure J. C. Huffman and A. P. Sattelberger J. Chem. Soc. Chem. Commun. 1985. 552. 203 Ti,Zr Hf;V Nb Ta; Cr Mo W; Mn Tc Re TaCl(C0)3(PMe3)3. This can be achieved by either the reaction of TaC1H2(PMe3h with CO or by the oxidation in ether solution of [Ta(CO),]- by TaCl in the presence of PMe,. The X-ray diffraction structural analysis of this molecule showed a capped trigonal prismatic arrangement with the chlorine atom in the capping position.The equivalent bromo- or iodo-product can also be produced by treating a mixture of Na(Ta(CO),) and PMe with either bromide or iodine. When repeated in the absence of phosphine only a bridged species [M2X3(C0)J was obtained.51 A number of reactions involving vandadium cyclopentienyl species interacting with nitric oxide have been in~estigated.~~ Many of the products were found to be polymeric in nature as for example when using (Cp),V(CO) which gave an insepar- able mixture of two products one of which was a complex containing an NCO group. With (Cp),VI two products also were obtained both formulated (Cp),VINO. One was a brown polymer and the other a green monomer that produced an interesting brown material after standing for a week in thf.X-Ray analysis showed that the product [{(Cp)VI},{ CpVNO};?( p -0)4],has eight-membered rings (6) stacked above each other. The 0-V-0 angles were all around 104.7' but the V-0-V angles alternate between near linear (179.3') and 148.1'. Use of the di-Grignard reagent {~-[(thf),,ClMgCH~]c~H~}~, in thf with the species [MC~,(CP)~] gave53 quite different results for M = V than for M = Nb or Ta. Vanadium gave a bimetallic complex while niobium and tantalum gave paramag- netic metallepines (Scheme 3). Finally some interesting tantalum(v) dithiolate complexes have been de~cribed.,~ By addition of Ta( T~-C,M~,)C~ to Na2S2C2H2 in thf the complex Ta( v5-C,Me5) (SCH=CHS)2 was formed. It was shown by 'H n.m.r.spectroscopy to be fluxional (Scheme 4)between two piano-stool arrangments. This allows good interactions to develop between the C=C and the vacant dX2-,,2 and d,2 orbitals. 4 Chromium Molybdenum and Tungsten The chemistry of these elements will be discussed under three main sub-headings. First any interesting points about binary compounds and polyanions will be con- sidered then coordination compounds and finally organometallic compounds. A stepwise mechanism for the thermal decomposition of (NH4)2[Mo2S13].nH20 to give MoS has been proposed.55 There is no change in the molybdenum oxidation 51 F. Calderazzo M. Castellani G. Pampaloni and P. F. Zanazzi J. Chem. SOC.,Dalton Trans. 1085 1989. 52 F. Bottomley J. Darkwa and P. S. White J. Chem. SOC.,Dalton Trans.1985 1435. 53 S. I. Bailey L. M. Engelhardt W.-P. Leung C. L. Raston I. M. Ritchie and A. H. White J. Chem. Soc. Dalton Trans. 1985 1747. 54 K. Tatsumi J. Takeda Y. Sekiguchi M. Kohsaka and A. Nakamura Angew. Chem. Znt. Ed. Engl. 1985 24 332. 55 A. Muller and E. Diemann Chimia 1985 39 312. J. E. Newberry I J Nb -thf I [MR2(CP)21+[BFJ-Reagents i [MCI(Cp),] thf -78 "C; ii AgBF, thf; iii NaBH, thf; iv Na(C,,H,) or Na/Hg 18-crown-6 thf; v HBF,.OMe, thf; vi [CPh,] BF, thf Scheme 3 Scheme 4 state and the reaction proceeds with the release of sulphur and 1 mol of hydrogen sulphide. The indicated structural relationship between discrete [Mo3S13]2- ions and crystalline Mo'" sulphide may be important in view of the widespread use of MoS as a catalyst in processes such as hydrogenation dehydrogenation and reductive etherification.Moving on to the 0x0-anions an orange-coloured tung- sten(rv) aquo ion [W3(p3-0)(p-0)3( H20)9]4+ has been prepareds6 by treating K2WC16 with 2M-HC1 followed by elution from a cation-exchange column with p-toluenesulphonic acid. M. Segawa and Y. Sasaki J. Am. Chem. SOC.,1985 107 5565. 205 Ti,Zr Hf;V Nb Ta; Cr Mo W; Mn Tc Re A review of structure electronic configuration and properties of polymolybdates has been p~blished.,~ One of the major features of the article is the interesting compilation of vibrational spectroscopic information including resonance Raman measurements. A C, structure is suggested” for the anions [MW@18S]3- where M = Ta or Nb by consideration of 170 n.m.r.and infrared spectroscopy. It contains a central plane of eight members (WO) surmounted on one side by (WO,) and on the other by (O,M=S). There are distinct differences between the tantalum and niobium species in both the 170n.m.r. signals and in the M=S vibrational frequency. Nuclear magnetic resonance spectroscopy is ideal for observing dynamic processes in these anions and has been used59 to study (Y-Mo~O:; PhAsMo,O:, and (PhAs),Mo,O;,. These species have a common (RX05-),(Mo6Ol8) structure (7) (7; RX = OMo OPAs) containing a central ring not unlike the smaller species discussed in the previous reference. The RXOZ-groups above and below the central ring are attached by weak molybdenum-oxygen bonds which facilitate some of the fluxional processes observed.A similar framework to (7) has also been found6’ in [M~~o~~(”ph),]~-. Alternate molybdenums in the central core carry two -NNPh groups instead of 0x0 groups and of course the X atom is a molybdenum. This structure has similar weaker Mo=O interactions between the capping moieties and the ring. Other applications of n.m.r. involving nucleii such as 170 31P,and 183W have included the study of [W7024]6- in a variety of conditions6’ and the evaluation of interaction strengths between alkali metal ions and the PWl103; ion.62 A series of vanadium-containing heteropolyanions have been studied by p~tentiometry.~~ Various species (PVnW12-n040)-3-n were obtained but always in the form of 57 R.I. Buckley and R. J. H. Clark Coord. Chem. Reu. 1985,65 167. 58 W. G. Klemperer and C. Schwartz Znorg. Chem. 1985 24,4459. 59 W. G. Klemperer C. Schwartz and D. A. Wright J. Am. Chem. SOC.,1985 107 6941. 60 T.-C. Hsieh and J. Zubieta J. Chem. SOC.,Chem. Commun. 1985 1749. 61 R. I. Maksimovskaya and K. G. Burtseva Polyhedron 1985,4 1559. 62 R. I. Maksimovskaya M. A. Fedotov and G. M.Maksirnov Russ.J. Znorg. Chem. (Engl. TransL) 1985 30,514. 63 A. K. Akhmetova and A. K. Il’yasova Russ. J. Inorg. Chem. (Engl. Transl.) 1985 30,504. 206 J. E. Newberry mixtures. Related material xH20. [PV,MO~~-,,O~~]H~+~ has been dehy- n = 0-3 drated and reh~drated.~~ In particular the time dependence of rehydration was followed by vibrational spectroscopy.Coordination Compounds.-There was a good crop of review articles relevant to Group 6 coordination compounds last year. One thoughtful account was on Cr"' and the so-far unidentified complex glucose tolerance factor.65 The factor is believed to be present in meat brewers' yeast and certain other foods. Much information on various metabolic experiments in both animals and humans is included in this article. The link with glucose tolerance and diabetes comes from observations of raised chromium urine levels in patients with diabetes. Several suggestions for suitable structural types involved in the factor are made. On more mainstream coordination matters a massive compilation (264 references) has been reported66 on the coordination chemistry of chromium(v).Structural and kinetic aspects are the main concern. In a review of seven-coordinate molybdenum complexes it was noted67 that despite the complicated geometry good progress has been made in structural analysis. Most of the examples involve monodentate and bidentate ligands. A large part of the interest in molybdenum comes from its major role in biology as an essential component of many important enzymes and co-factors. From gout to bovine copper-molybdenum antagonism and nitrogen fixation the special areas of interest have been carefully expressed in a useful article.68 From this broad sweep to a much more selective approach and two short that have been published on the coordination chemistry of SzN2 and chloronitrene complexes.Both cover the entire array of metals but are mainly concerned with molybdenum and tungsten. The chloronitrene complexes in particular are commended as excellent starting materials for the preparation of new M=N species. A good range of oxomolybdenum(1v) complexes have been examined7' by 95M0 n.m.r. spectroscopy. The chemical shifts covered a wide range from 1035 p.p.m. for [MoOCI(CNMe)J to 3 180 p.p.m. for [MoOCl,(phen)PPh,Me]. Interesting trends can be discerned for variation in ligand type and coordination numbers. N.m.r. signals from 95M0 can be collected72 from MoSi- in contact with bovine serum albumin at natural abundance levels of molybdenum. The signal quality was improved by using an enriched sample but the main point of interest was the apparent ability to measure the number of metal ion binding sites on the albumin.A detection limit of ca. 10p.p.m. and the known sensitivity of Mo chemical shifts to the environment indicate that n.m.r. spectroscopy can be used to study molyb- denum-containing co-enzymes. 64 C. D. Ai P. Reich E. Schreier H.-G. Jerschkewitz and G. Ohlmann 2. Anorg. Allg. Chem. 1985 526 86. 65 J. Barrett P. O'Brien and J. Pedrosa de Jesus Polyhedron 1985 4 1. 66 M. Mitewa and P. R. Bontchev Coord. Chem. Rev. 1985 61 241. 67 M. Melnik and P. Sharrock Coord. Chem Rev. 1985 65 49. S. J. N. Burgmayer and E. I. Stiefel J. Chem. Educ. 1985 62 943. 69 K. Dehnicke and U. Muller Comments on Znorg. Chem. 1985 IV 213. 70 K. Dehnicke and U. Muller Transition Met.Chem. 1985,10,361. 71 C. G. Young and J. H. Enemark Inorg. Chem 1985 24 4416. S. Bnstow C.D. Gamer S. K. Hagyard G. A. Morris J. R. Nicholson and C. F. Mills J. Chem. SOC. 72 Chem. Commun. 1985 479. Ti,Zr Hf;V Nb Ta; Cr Mo W; Mn Tc Re 207 Starting with specific coordination compounds nitrogen donor ligands will be considered first. Important work continues in the area of dinitrogen complexes. Reduction under nitrogen of WC14(PMe3) gives cis-[W( N2),(PMe3)J or trans-[W(C2H4)2(PMe3)4] if carried out73 under an ethene atmosphere (Scheme 5). The structure of [W( C2H4)2 (PMe,),] was determined by X-ray diffraction analysis and shows an essentially octahedral metal with trans ethene groups that adopt the advantageous mutually perpendicular orientation.cis-[W( N2)2(PMe,),)] -trans-[W( C2H4)2( PMe,),] iv vi! I // all-trans-[ W(C2H4)2(CO)2( PMe,),] W(N,)(PMe,L / trans,rner-[W(C2H4)2(CO)(PMe,),] Reagents i Na reduction thf N2; ii Na reduction thf C,H4; iii C2H4 hv; iv PMe3 Ar; v CO 1 atm; vi CO 3 atm Scheme 5 The preparation of the complex anion [MoCl,NSCl]- was reported last year and it has been shown to be a straightforward octahedral complex. There is a near-linear Mo=N=S configuration (171.2"). The Mo-C1 distances are all about 2.35 A in the equatorial plane but the axial chlorine shows a trans effect and is at 2.47 A. If W(CO)6 is refluxed in carbon tetrachloride with PhS02.NC12 then a good yield of C12W( NSO,Ph) is obtained." On recrystallization from acetonitrile crystals of the complex WC1,(MeCN),(NSO2Ph) were formed.It has a distorted octahedral arrangement with trans chloro-groups and a bond angle C1- W-Cl of 157.3". Although seven-coordinate complexes are quite common for molybdenum few involve the participation of terdentate ligands. It has been that if Mo(Cl),(EtCN) is reacted with Me3SiN3 in the presence of terpyridine then the complex MoN( N,),Cl(terpy) is produced. This has been studied by X-ray diffraction and found to have a distorted pentagonal bipyramidal structure with the triply-bound nitrogen in the axial position (1.66& Mo-N). This ligand exerts a strong trans- effect as shown by the long Mo-C1 bond (2.72 A) of the other axial species. In a related the complex Mo(NO)(N,),(terpy) was found to have a similar structure with the axial positions occupied by NO and one of the azide groups.The trans-effect was weaker here with Mo-N (axial) of 2.18 A being almost the same as MO-~3 (equatorial) at 2.12 A. 73 E. Carmona A. Galindo M. L. Poveda and R. D. Rogers Inorg. Chem. 1985 24 4033. 74 U. Muller P. Klingelhofer U. Kynast and K. Dehnicke 2. Anorg. AZZg. Chem. 1985 520 18. 75 H. W. Roesky J. Sundermeyer J. Schimkowiak P. G. Jones M. Noltemeyer T. Schroeder and G. M. Sheldrick Z. Naturforsch. Teil B,1985 40 736. 76 J. Beck E. Schweda and J. Strahle 2. Nuturforsch. Teil B 1985 40 1073. 77 J. Beck and J. Strahle 2. Nuturforsch. Teil B 1985 40 891. J. E. Newberry In view of the position of chromium in metabolic processes it is important to observe the types of interaction possible with biologically significant molecules.Amongst these many of the most useful are N,O-donors. The molecule (L-alanine-N- acetato) (L-histindinato)Cr"'H,O can exist in six isomeric forms and crystals of one of these have been examined ~tructurally.'~ It was found to be (R)-L-truns(O)cis(N) having a slightly distorted octahedral shape with cis-angles between 80 and 99'. Moving on to oxygen donors it is appropriate to start with a peroxo-complex K2[WO(02)2(C,04)]. This has been found79 to be a pentagonal bipyramidal structure (8) with the peroxo-groups in the equatorial plane. The oxalate group has a small internal twist (6.9') and spans the equatorial and axial positions with W-0 (equatorial) of 2.03 8 and W-0 (axial) of 2.24 8,.In common with similar species the tungsten is raised from the equatorial plane towards the axial oxygen. 0 0 Tetrahydrofuran has been used to stabilize molybdenum(rI1) to give a material that is soluble in non-aqueous solvents. The complex MoCl,(thf) is soluble only in thf and is thus of limited synthetic application. Zinc reduction of MoCl,(thf) gives an anionic species [MCl,(thf),]- which has been shown" to have near octa- hedral (D4,,symmetry) structure in the solid state. The solid is air-stable and is soluble in a wide range of donor solvents. A review on the glucose tolerance factor and a link with chromium( 111) has already been One of the favourite suggestions for the metal environment is in a complex involving amino-acids.An enterprising approach to this problem has been reported" with the synthesis of a series of mixed-ligand complexes between the tripeptide ligand H4L-(9) glutathione and one of the amino-acids glycine cysteine or glutamic acid. From a consideration of this series of species by a number of techniques of which circular dichroism was the most useful it was possible to 78 M. Sato M. Kosaka and M. Watabe Bull. Chem. SOC.Jpn. 1985 58 814. 79 R. Stomberg and S. Olson Acta Chern. Scnnd. Teil A 1985 39 79. 80 A. Hills G. J. Leigh J. Hutchinson and J. A. Zubieta J. Chern. Soc. Dalton Trans. 1985 1069. 81 M. Abdullah J. Barrett and P. O'Brien J. Chem. SOC.,Dalton Trans. 1985 2085. Ti Zr Hf; V Nb Ta; Cr Mo W; Mn Tc Re show that glutathione is bound by the (N,O) of the terminal glycine and by the deprotonated sulphur of cysteine.The glutamic acid residue is not involved. Reaction of excess Me2S with MoBr formsg2 red crystals of the slightly moisture- sensitive material MoBr (SMe,),. This was found to be octahedral with the sulphur ligands in the trans configuration and angle S-Mo-S of 180" exactly. Molyb- denum(rv) complexes are usually of at least coordination number six but by using bulky groups it was possibles3 to produce near-tetrahedral species Mo( SR)4 where R = 2,4,6-trimethylbenzene (or the equivalent isopropyl species). These were synthesized by reacting MoCl,(thf) with NaSR under argon. There is a major difference between the two complexes in their electrochemical behaviour in dimethoxyethane.The methyl complex has a quasireversible redox couple (E; us. SCE) at -0.07 V whereas with the isopropyl ligand the couple is at +0.32 V. The ferrocenecarbodithioate ligand (lo) (L) has been showng4 to produce a number of molybdenum complexes such as MoIVOL2 M03(03L4 and MoV1O2L2. The MoV compound was found to disproportionate in solution. Cyclic voltammetric observations identified quasi-reversible couples for the other complexes and also indicated that several of the oxidized species were of considerable stability. A large number of seven-coordinate complexes have been investigatedg5 by 95M0 n.m.r. spectroscopy. The linking factor was that most were dithiocarbamates. The chemical shifts ranged from -437 p.p.m.for Mo(NO)~(S,CNM~~), to +182 p.p.m. for MoOBr,( S2CNEt2),. Some 14N n.m.r. resonances were also recorded. These show little change with the nature of the alkyl group of the dithiocarbamate but quite strong alterations with the other ligand. Chemical shifts ranged from -14 p.p.m. for Mo(NO)(S,CNMe,) to 42 p.p.m. for Mo(NS)(S,CNM~,)~. The line width of the 95M0 line is however strongly affected by the dithiocarbamate. The complexes C~-MOO,(S~CNR~)~ have a much greater line width (roughly an order of magnitude) than [MOO( S,CNR2),]- and both series show a linear relationship with the alkyl chain length. An interesting series of mixed-ligand tungsten( ~v) complexes has been described.g6 The species were formed by using the ligand 2-mercaptopyrimidine (L) and 5-t-butyl- 2-mercaptopyrimidine( L') and were formulated WL LiPn.The complexes were separated by preparative scale TLC on silica gel plates. A pair of stereoisomers was 82 C. Schurnacher R. E. Schmidt and K. Dehnicke 2. Anorg. Allg. Chem. 1985 520 25. 83 N. Ueyama H. Zairna and A. Nakarnura Chem. Lett. 1985 1481. 84 M. Nakamoto K. Tanaka and T. Tanaka Bull. Chem. SOC.Jpn. 1985 58 1816. 85 M. Minelli C. G. Young and J. H. Enemark Inorg. Chem. 1985 24 1111. 86 C. J. Donahue E. C. Kosinski and V. A. Martin Inorg. Chem. 1985 24 1997. 210 J. E. Newberry found for the n = 2 formulation. The 'Hn.m.r. spectra indicate that the complexes are rigid in that time scale and the measured spectra have been interpreted in terms of the implied solution stereochemistry.By determining the cis:trans ratios of the product W(CO),(L)(L') obtained by reacting one of series of twelve phosphines (L') with W(CO),( L)py it was hopedg7 to compare the effect of the cone angle of the phosphine. The main conclusion was that in general the ratio variation observed was in line with the assumed cone angle except for PEt and PBui. Both of these are underestimated by about lo" a situation that results from the assumed conformation of the phosphine used for the cone angle description being different from that actually adopted by the ligand. The co-condensation of molybdenum atoms with trimethylphosphine has been showngg to give the complex Mo( PMe,),. As expected this electron-rich species is exceptionally valuable as a starting point for the synthesis of a whole range of low-valent compounds (Scheme 6).N Ill Mo (atoms) Me3P\ I /PMe3 + PMe3 Me3P PMe3 PMe3 L HZCTCH2 0 iii Mo(PM~~)~-Me3 Me3 PP H\\! r/H HzCfCH2 Me P 2M P M e3 HMO. \\ /PMe3 Me3P /I\ PMe3 PH cM0\pMe3 Me3 Reagents i Co-condensation followed by recrystallization; ii dinitrogen (15 atm) 48 h; iii ethene (3 atrn) 18 h; iv cyclopentadiene 3 d; v butadiene (3 atm) 12 h; vi hydrogen (3 atm) 3 d; vii carbon monoxide (2 atrn) 5 min Scheme 6 The final set of papers to be considered in this section on mononuclear coordina- tion compounds of Group 6 is that involving macrocyclic ligands. The most interest- ing of these ligands are the porphyrins.Chromium( 11) porphyrin complexes have been showng9 to react irreversibly with oxygen in both solution and the solid state to give CrIvO(por). 87 M. L. Boyles D. V. Brown D. A. Drake C. K. Hostetler C. K. Maves and J. A. Mosbo Inorg. Chem. 1985 24 3126. xa M. Brookhart K. Cox F. G. N. Cloke J. C. Green M. L. H. Green P. M. Hare J. Bashkin A. E. Derome and P. D. Grebenik J. Chem. SOC.,Dalfon Trans. 1985 423. a9 D. J. Liston and B. 0. West Inorg. Chem. 1985 24 1568. Ti,Zr Hf;V Nb,Ta; Cr Mo W; Mn,Tc Re 21 1 It was also possible to isolate an unstable p-0x0 complex (tpp)CrOCr(tpp) where tpp is tetraphenylporphyrin. The p-0x0 linkage can be detected by infrared absorp- tion at 860 cm-' and also by magnetic characteristics which show coupling between the Cr'" centres.Coupling was also studied between Cr"' and Fe" porphyrins." Not all chromium(II1) porphyrins are dinuclear and Cr"'Cl(tpp) has been shown'' interact with a wide range of thiolate ligands. This leads to the development of unusual bands in the electronic absorption spectra. Thioglycolate esters were used as the ligating species and it is suggested that the spectral changes indicate a similar environment to that found in the reduced cytochrome P450-CO complex Related solvent effects in MoVO(tpp)X (X = F Cl Br) have been observed?2 Solvents are classified as either coordinating (in an axial position) or as non- coordinating. Dichloromethane was found to be non-coordinating and alcohols pyridine aniline etc.were found to be coordinating. For X = C1 photoirradiation in the visible region caused93 the absorption spectrum to alter gradually to that of MoIVO(tpp). E.s.r. spectral evidence suggests that the reaction may proceed by homolytic cleavage of the Mo-C1 bond followed by reaction of the C1* radical with the solvent. Cluster Compounds.-The information in this section will be considered grouped around the nature of the ligand species starting with binuclear bridged complexes and moving on to larger clusters and finally to those with extensive metal-metal bonding. Treatment of WC16 with N(SiMe3)3 followed by addition of PPh4C1 has been shown94 to give a brilliant red powder formulated PPhJ W2NCl,o] (Scheme 7). This has octahedral tungsten centres (WCl,) linked via a W-N-W bridge that is not quite linear (173").The nitrogen was found to be asymmetrically positioned with W-N of 1.79 and 1.88 A. Addition of carbon tetrachloride to a dichloromethane solution of this species produ~es'~ red crystals of a related trimer [WC15(p N)WCl4(p-N)WCl5I2-. This is quite similar in structure with W-N-W angles of 176.0 and 175.2" and also asymmetric with (W-N = 1.81 2.12 and 1.86 2.01 A). The equatorial chlorines of the three tungsten atoms take up a mutally eclipsed configuration. WC1 -!+ W,NCI, 1 ii PPh,[W2NCl,ol 1 iii (PPh4)2[W,N,Cl,,I Reagents i N(SiMe,),; ii PPh4Cl; iii CCI Scheme 7 90 D. J. Liston B. J. Kennedy K. S. Murray and B. 0. West Znorg. Chem. 1985 24 1561. 91 H. Sakurai J.Tamura and T. Yoshimura Znorg. Chem. 1985 24 4227. T. Imamura T. Tanaka and M. Fujimoto Znorg. Chem. 1985 24 1038. 92 93 T.Imamura T. Jin T. Suzuki. and M. Fujimoto Chem. Lett. 1985 847. 94 Th.Godemeyer A. Berg H.-D. Gross U. Muller and K. Dehnicke 2.Naturforsch. TeilB 1985,40,999. 95 Th.Godemeyer K. Dehnicke and D. Fenske 2. Naturforsch. Teil B 1985 40,1005. J. E. Newberry Reaction of (NSC1)3 with any of a wide range of chromium species (Cr metal Cr(C0)6 CrC13.3thf or Cr"' oxide) is known to give species containing the ion [CrC14N2S2]-as the main product. However furtheq6 treatment of a dichloromethane solution with AsPh4C1 gave a complicated species (AsPh4),- [CrC1,(p-N2S2)],. This has virtually a square of chromium atoms with each pair of metals bridged by a near-planar N2S2 placed perpendicular to the square (1 1).The crystals were characterized by both X-ray diffraction and infrared spectroscopic investigations. A rather different type of nitrogen donor was in the next study (12). It was observed that the metal-ligand charge-transfer energy decreases as the size of the central group [R in (12)] also decreases. A good linear plot was obtained for the graph of the reduction potential Et us. MLCT (metal-ligand charge-transfer frequency). This behaviour implies strong interaction between the LUMO orbitals of the two molybdenum a,a'-diimino moieties. Increased interaction between the sites gives a decrease to the LUMO energy. It has been claimed 98 that the oxygen bridged (OzM-O-M02)2+ core can be readily identified in a whole range of known species by the observation of a signal at ca.120 p.p.m. in the 95M0n.m.r. spectrum. This should aid the study of interconver- sions in solution. The anion of 6-methyl-2-hydroxypyridine mhp takes99 a strange style of bridging mode in the complex Cr4(0H)4(mhp),. The complex was formed by refluxing Cr(C0)6 and Hmhp in diglyme. An X-ray diffraction analysis revealed the presence of a central cubane-like core of alternate Cr and OH groups. The cube was found to be only slightly distorted with Cr-0 equal to 1.93 f0.02 A. The mhp ligands are present in two styles. Four of them act as bridges to chromium atoms across the diagonals by using the (0,N) donor capacity of this ligand.The other four ligands are uniquely bound to one metal uia the oxygen and the nitrogen is linked by a hydrogen bond to the hydroxyl species present in the cubane core. Each chromium then becomes essentially octahedral. The main bridging oxygen ligands with these Group 6 metals are alkoxides but most of these will be dealt with later under cluster compounds and metal-metal 96 H. Wadle K. Dehnicke and D. Fenske 2.Nafurforsch. Teil B 1985 40 1314. 97 M.-A. Haga and K. Koizurni Inorg. Chim. Acfa 1985 104 47. 98 B. Piggott S. F. Wong and R. N. Sheppard Inorg. Chim. Acfu 1985 107 97. 99 L. Akhter W. Clegg D. Collison and C. D. Gamer Inorg. Chem. 1985 24 1725. Ti Zr Hf; V Nb Ta; Cr Mo W; Mn Tc Re 213 bonded species. As an example of further progress in the more straightforward bridging mode the reported structure of [WNPh(p-OMe)(OMe)3]2 may be examined with profit."' There is asymmetric bridging (W-0 of 2.05 and 2.16 A) and these ligands with another methoxide and the imido group form the equatorial plane about each metal.The imido groups are mutually trans across this bridge. It is quite interesting to note that on moving down the periodic table from oxygen to sulphur donors the tendency for the ligand to be found mainly in metal-metal bonded clusters is much diminished. Most of the sulphur donors are found in bridged species that are held together solely by metal-ligand interactions. As a paradigm consider the cubane-like (T&M~~)C~~CO~(CO)~S~. The carbonyl group on the cobalt atoms can be replaced stepwise by tertiary phosphines and it has been shown,"' by X-ray diffraction work that the 60-electron cubane core is retained.In a related fashion the double-cubane [(Mo( FeSEt),S,),( P-SE~)~]~- sheds the six terminal -SEt groups when treated with phenol.lo2 A slight blue-shift occurs in the optical spectra but the magnetic properties are virtually unaffected. One reason for the interest in such species is the insight that can be gained into molybdenum sites present in various proteins. This may involve charge calculations or examination by various X-ray techniques. For example a molecular-orbital Fenske-Hall study on [Ni( MoS,)~],- and [Ni( MoS,O,)~]~- has shown'03 that the HOMO/LUMO differences are consistent with the redox values.Results from an examination of the Mo K-edge X-ray absorption edge and near edge structure (XANES) have also been ~ollated.''~ The use of X-ray absorption spectra has most commonly involved the study of extended fine structure (EXAFS). The XANES region represents that part of the X-ray absorption spectrum from the onset of the absorption discontinuity up to the start of the EXAFS zone. It tends to give information on the absorbing atom and is thus complementary to EXAFS which is more useful for probing the coordination sphere of the absorber. A good range of single and double cubanes was examined and it was suggested that the best fit to the spectrum given by nitrogenase was attained by clusters involving a M0S303 moiety. One difficulty found in this type of study is at the final stage when the results from model systems have to be compared to those from the dilute biological sample.The general assumption that heavy elements are stronger backscatterers than lighter elements does not always hold in EXAFS. Thus in comparing a number of tungsten clusters with their molybdenum analogues it was fo~nd''~ that peaks due to known Fe-W environments were missing from the Fourier transforms of the Fe EXAFS data. Tungsten has two minima in the backscattering amplitude range that occur in the area important for structural detail. Factors such as these become especially important when obtaining spectra from biological samples where the relative intensities are expected to be low. LOO A. J. Nelson J.M. Waters and D. C. Bradley Polyhedron 1985 4 285. I01 H. Brunner W. Meier J. Wachter H. Hsterer and M. L. Ziegler Z. Nuturforsch. Teil B. 1985,40,923. 102 W. E. Cleland Jr. and B. A. Averill Znorg. Chem. Acta 1985 107 187. 103 L. Szterenberg and B. Jezowska-Trzebiatowska Bull. Pol. Acud. Sci. Chem. 1985 33 295. S. D. Conradson B. K. Burgess W. E. Newton K. 0. Hodgson J. W. McDonald J. F. Rubinson S. F. Gheller L. E. Mortenson M. W. W. Adarns P. K. Mascharak W. A. Armstrong and R. H. Holm J. Am. Chem. SOC.,1985 107 7935. lo' M. R. Antonio B. K. Teo and B. A. Averill J. Am. Chem. Soc. 1985 107 3583. 214 J. E. Newberry A wide range of spectral chacteristics (ix. Raman resonance Raman u.v. and XPS) have been measuredlo6 for a series of cyanothiomolybdates.These have central units not unlike that found in ferredoxins. The compounds chosen represented a gradation in electronic charge and structural type (Scheme 8). The anions investi- gated were [Mo,S,(CN),]"- n =4 or 6 Mo"' or Mo'" (8a); [Mo,S(CN),,]~- Mo'" (8b); [Mo,S,(CN),]'- Mo'" (8c); and [MO~S~(CN),,]~-, Mo"' (8d). I/ I/ -Mo-S-MO-/I 'I \/ S-Mo' \I /\ Scheme 8 Mo-S skeletons of some cyanothiomolybdates There are also Mo-S clusters that have significant metal-metal bonding present. For example both Mo,S:+ and Mo,S;+ species have been recently inve~tigated.'~~~'~~ The tetranuclear ion was found to have a central Mo~ unit. Rather interestingly this does not adopt a tetrahedral arrangement but is C,,with basal Mo-Mo distances of 2.87 8 and Mo-Mo (slant edge) of 2.79 A.A short review on hexa-alkoxides of Mo and W has been p~blished.''~ Various alkyne cyano- and carbonyl adducts with these MEM species are discussed but no evidence is presented that points to any dinitrogen involvement. A review of 'electron-rich' MEM species with the configuration a27r4S26*2has also been published."' This deals mainly with Moi+ and Re:+. The nomenclature refers to the species 027r4S2and either the addition of 2 electrons to give the 'electron-rich' configuration above or the subtraction of 2 electrons to give the S27r4electron-poor species such as found in the Mo;+ core of the hexa-alkoxides. There is much structural detail and a discussion of their interesting electrochemical features.In the M-M 'paddle-wheel' tetra-carboxylates most of the structural information ccnnes from X-ray diffraction analysis. This is not the best situation if it is intended to use the results in any theoretical calculations since it is known that the M-M bond distance is exceptionally sensitive to any axial perturbation. Hence the gas- phase electron-diff raction analysis of Cr2(O,CMe) provides"'usefu1 information. 106 A. Muller R. Jostes W. Eltzner C.3. Nie E. Diernann H. Bogge M. Zirnmermann M. Dartmann U. Reinsch-Vogell S. Che S. J. Cyvin and B. N. Cyvin Inorg. Chem. 1985 24 2872. F. A. Cotton Z. Dori R. Llusar and W. Schwotzer J. Am. Chem. SOC.,1985 107 6734. 108 F. A. Cotton M. P. Diebold Z. Dori R. Llusar and W. Schwotzer J. Am. Chem. SOC,1985,107,6735.109 M. H. Chisholm D. M. Hoffman and J. C. Huffman Chem. SOC.Rev. 1985 14 69. 110 R. A. Walton Israel J. Chem. 1985 25 196. 111 S. N. Ketkar and M. Fink,J. Am. Chem. SOC.,1985 107 338. Ti Zr Hf;V Nb Ta; Cr Mo W; Mn Tc Re It shows that Cr-Cr is 1.966 A which differs markedly from the value of 2.03 8 found in the solid state which was determined by X-ray diffraction. This situation has been further discussed112 in a paper on bonding in related tungsten compounds. In particular relativistic Xa-SW calculations were made on W2(02CR) and W2(02CR)4Ri. The results suggest an interesting idea that the second formulation should not be regarded as a WEW moiety having axial anionic ligands but as a neutral WEW species interacting with alkyl ligands.This is consistent not only with the calculations but also with observations of the photo- chemical behaviour and trends in the metal-metal bond length for such compounds. Non-carboxylate complexes of the type Mo2X8 will also mainly take up the paddle-wheel configuration except it is better described as the eclipsed conforma- tion. However if some of the unidentate ligands are replaced by bidentate species then a partially staggered form may be adopted. This situation allows studies to be made on how electronic absorptions or bond lengths are affected by the degree of twist (x)about the bond. Thus a correlation between the S +S" transition and cos (2x)has been for a series of MO~X~(LL)~ compounds where X is C1 or Brand LL is mainly a diphosphine.While the trend is clear correlation coefficients for such plots tend to be rather low unless some account is made" of alterations in electron withdrawing and donation effects from some of the substituents on the ligands. These corrections are essentially empirical but do give significant insights. Tungsten analogues to the molybdenum tetra-carboxylates are of comparatively recent origin. An examination' of the electrochemical characteristics of W2(O2CBu') and W(02CMe) by cyclic voltammetry shows that the molybdenum species are much harder to oxidize with E; about 0.75 V more positive than the tungsten compounds. This large difference has clear implications for the type of experimental procedures used in this area of work. Continuing on the trail of these metal-metal bond compounds the hexa-carboxy- lates of tungsten demonstrate an interesting point about the nature of the axial position.The species W2(02CB~f)6 has been shown' l6 to be essentially pentagonal bipyramidal about each metal (13). Two of the ligands are in the bridging mode while the other four are each associated with only one metal. However the ligand that spans the axial and the equatorial positions shows a very large discrepancy in 112 M. D. Braydich B. E. Bursten M. H. Chisholm and D. L. Clark J. Am. Chem. Soc. 1985 107 4459. 113 F. L. Campbell 111 F. A. Cotton and G. L. Powell Znorg. Chem. 1985 24 177. 114 F. L. Campbell 111 F. A. Cotton and G. L. Powell Znorg. Chem. 1985 24 4384. 115 D. J. Santure J. C. Huffman and A.P. Sattelberger Znorg. Chem. 1985 24 371. 116 M. H. Chisholm J. A. Heppert D. A. Hoffman and J. C. Huffman Znorg. Chem. 1985 24 3214. J. E. Newberry the W-0 bond lengths. The axial distance is around 2.5 A whereas the equatorial is 2.07 A. This latter distance is even shorter than the 2.1-2.15 A (W-0) of the other ligands in both bridging and non-bridging modes. It thus seems that the ligand is attached only very loosely in the axial position. This could well reflect a reluctance to bind in a position that would compete for electrons in the M-M bond. It should also be noted that the ligands in the pentagonal planes adopt a mutually eclipsed conformation. This pattern of eclipsed ligands in both bridging and non-bridging modes cannot always be attained.In the reaction of &Mo2C18 with bidentate tertiary phosphines to give MO&~,(LL)~,the presence of both bridging and nonbridging modes has been recognized. It is claimed"' that the bridging mode is favoured by reactions carried out in higher alcohols whereas the non-bridging mode is favoured from methanol. The presence or absence of isomeric forms of certain adducts has been"' ascribed to variability in the starting material. When Mo2(02CCF3) is reacted with 2 equivalents of PR3 there have been reports of the formation of axial and equatorial products (14). The axial mode is favoured when PR is very bulky but with PMe or PEt the equatorial situation is preferred. There are six isomers possible for this position but it is now suggested that only the C, core (14) form is produced.Previous reports of a mixture of equatorial isomers may well owe their origin to the presence of Mo2(02CCF3),(02CMe)in the starting material. I P O/c\ L,l /o-j-c\ O/L\I 0 /o-/T / o$/ \ /cTo/p\ o$37-O /To\. /O 0 I \c/o I I (14) Various complexes can be i~olated"~ are if toluene solutions of Mo~C~~(NM~~)~ treated with tertiary phosphines. The bidentate phosphines tend to give kinetically inert 1:1 species that probably have bridging ligands while the unidentate can give two forms depending on temperature (Scheme 9). When repeated with tungsten instead of molybdenum similar products were formed but at slower rates. One major difference noted was that the complex Mo2C1,( NMe,),L is capable of reaction with further phosphine ligand to give Mo,Cl,L, but this was not found to occur with the tungsten species.117 N. F. Cole D. R. Derringer E. A. Fiore D. J. Knoechel R. K. Schmitt and T. J. Smith Znorg. Chem 1985 24 1978. 118 D. J. Santure and A. P. Sattelberger Znorg. Chem. 1985 24 3477. 119 K. J. Ahmed M. H. Chisholm K. Folting and J. C. Huffman Inorg. Chem. 1985 24 4039. Ti,Zr Hf;V Nb Ta; Cr Mo W; Mn,Tc Re (Me,N),CIMo-MoCl( NMe,) (LL)T i Mo2C12(NMe2)4 A \ (I-1 Mo,C~,(NM~,)~.L,4 Mo,C14( NMe2)2.L2 Reagents i toluene; (LL) = Me2PCH2PMe2; ii 25 "C toluene; L = PMe, PMe2Ph; iii 50 "C toluene; L = PMe2Ph; iv 60°C toluene Scheme 9 A similar final product Mo2Br4(PMe3),+ is also attained'20 by reacting MO~B~~(CH~S~M~,)~ with excess PMe,.It was produced by stirring green crystals of the initial product Mo~B~~(=CHS~M~,)~( PMe3)4 in toluene for ten hours. A number of cluster compounds have been formed from binuclear metal-metal bonded compounds. Thus in attempting to produce a nitrido complex by reacting w2(oPr')6(py)2 with (Bu'O),WZN an imido cluster was obtained instead.I2' This was shown (15) to be W3(p-NH)(OPri)lo and to comprise a triangular W-W framework (W-W = 2.56 8 av.). It is formulated as an imido species even though the proton was not located by the X-ray diffraction analysis. There is supporting evidence from infrared spectroscopy and 'H n.m.r. studies. RO OR \/ w\ / i'N'\OR RO-W&-\ 'W /,OR / '0' R 'OR RO A similar structure to that in (15) was also given'22 by the blue crystalline product of the reaction between W2(OPr')6(HNMe2)2 and WO(OPr'),.This material was formulated W30(0Pri),o and has a capping 0x0 group instead of the -NH. Hexa-alkoxides have also been shown'23 to abstract fluorine from PF3. If Mo~(OBU~)~ is refluxed with 2 mol equivalents of PF3 then a tetranuclear product can be isolated (Scheme 10). The structure of both the tetranuclear species and the dinuclear product after further reaction with PMe, were checked by X-ray diffraction in the solid state and nuclear magnetic resonance spectroscopy in solution. The tetranuclear material has one Mo-Mo of 2.26 A and the other of 2.63 A. The final product adopts a partially staggered conformation and has Mo-Mo of 2.27 A.120 K. J. Ahmed M. H. Chisholm and J. C. Huffman Organometallics 1985 4 1168. 121 M. H. Chisholm D. M. Hoffman and J. C. Huffman Znorg. Chem. 1985,24,796. 122 M. H. Chisholm K. Folting J. C. Huffman and E. M. Kober Znorg. Chem. 1985 24 241. M. H. Chisholm D. L. Clark and J. C. Huffman Polyhedron 1985 4 1203. J. E. Newberry RR R ROO 0 0 \/ Mo,(OBu') A Ro'b / \ I? OR Reagents i reflux with PF3; ii PMe Scheme 10 Other significant cluster ions that have been investigated this year [Mo3(tc3-O)(tc-C1)3(~-O2CH)3C13I- [W302(0AC)6(H20)3I2+ and [w3(p-o)-(CMe)(02CMe)6(H20)312+. Organometallic Compounds.-Starting with carbonyl complexes there have been a number of useful review articles published.One of these'27 discusses the photo- chemistry of compounds containing metal-metal bonds and is largely concerned with Group 6 and 7 metals. The authors point out that knowledge of electronic structures is still rudimentary and that any new system considered may produce results that are not predictable from the currently fashionable frameworks. Another review12* deals with what at first sight is a quite restricted area arene- Cr(C0)3 complexes. However the author demonstrates that there is a great deal of useful information to be discussed. Obviously bonding and conformations are central to the case but from this core an examination is made of charge-transfer complexes and also how reactions at the arene are controlled.Nuclear magnetic resonance spectroscopy is widely used to study carbonyl species. For example,'29 if Mo(CO)~ in dimethyl sulphoxide is treated with NaX then anions such as [Mo(CO),X]- can be produced. The 95M0resonances were found to cover a range of over 1000 p.p.m. with decreasing de-shielding in the order H-> CN-> NCS-> N; > Cl-> 02N-> F-. One of the recent innovations has been the increasing access to solid-state n.m.r. spectrometers. An examination of solid-state 170 and 13C n.m.r. signals has been made'30 for M(CO)6 M = Cr Mo or W. The tensor elements of the resonances were determined and showed rather high anisotropies for 170 that ranged from AS -691 p.p.m. for Cr to -619 p.p.m. for W. The I3C anisotropies were smaller and covered a narrower range (-421 p.p.m.for Cr to -393 p.p.m. for W). I24 L. Xian-Ti H. Jin-Ling and H. Jian-Quan Actu Chem. Sinica 1985 43 718. 125 A. Bino and D. Gibson Inorg. Chim. Actu 1985 104 155. 126 F. A. Cotton Z. Dori M. Kapon D. 0. Marler G. M. Reisner W. Schwotzer and M. Shaia Inorg. Chem. 1985 24 4381. 127 T. J. Meyer and J. V. Caspar Chem. Reu. 1985 85 187. ''* A. Solladii-Cavallo Polyhedron 1985 4 901. 129 E. C. Alyea A. Malek and J. Malito Inorg. Chim. Acta 1985 101 147. 130 E. Oldfield M. A. Keniry S. Shinoda S. Schramm T. L. Brown and H. S. Gutowsky J. Chem. Soc. Chem. Commun. 1985 791. Ti,Zr Hf;V Nb Tu; Cr Mo W; Mn,Tc Re Two groups have reported the photochemical synthesis of Cr(CO),( H2) in solu- tion.The hexa-carbonyl was dissolved in liquid xenon doped with dihydrogen and subjected to U.V. photolysis. An infrared absorption at 3030 cm-' was ~bserved'~' from the coordinated hydrogen and on repetition with deuterium shifted to 2241 cm-'. The complex is thermally unstable and decays'32 with a rate coefficient of 2.5 s-'. Although R,P=X (X = 0,S or Se) ligands have been widely used in coordination chemistry there are few examples of the equivalent tellerium species. If M(CO)6 M = Cr Mo or W is photolysed in thf in the presence of R,FTe then dark red crystals of M(CO),(R,FTe) are formed.'33 The structure of the tungsten compound was determined by X-ray crystallographic methods and shows a very short (1.92 A) W-C distance for the trans carbonyl. The '25Te n.m.r.resonance shifts downfield from the un-coordinated ligand (8 = -839 p.p.m. for ligand; S = -635 -749 -770p.p.m. for Cr Mo and W respectively). A selenium donor complex ion [W2(CO),,Se4]2' is formed when W(CO)6 is treated with Se4(Sb2F11)2 in liquid sulphur dioxide. Shiny black flat crystals were after the SO2 was evaporated and these have been shown by X-ray diffraction to have the structure shown (16). The central section (W2Se4) adopts a chair-like formation with W-Se of cu. 2.62 A. It really represents two sections [W(C0),Se2]+ that dimerize through long (3.02 A) Se-Se interactions. 0 An unusual role for bismuth is shown'35 in (17) for the compound W2(C0)8(p2-~2- Bi2)(p- BiMe)W(CO),. This was produced in low yield by reacting (Me3Si)2CHBiC12 with Na,[W(CO),] in thf.It is notable for the Bi2 species acting as a four-electron donor and is claimed as the first example of a monomeric RBi ligand. The Bi-Bi separation of 2.80 A is considerably shorter than that found in either Ph4Bi2 (2.99 A) or elemental bismuth (3.07 A nearest neighbour). Thiobenzaldehyde ligands can be prepared'36 by the reaction shown in Scheme 11. Sulphur insertion occurs in the M=C(H)R bond to form the moiety M(S=C(H)R). The ligand has the capability of bonding in a V'-fashion through 131 R. K. Upmacis G. E. Gadd M. Poliakoff M. B. Simpson J. J. Turner R. Whyman and A. F. Simpson J. Chem. SOC.,Chem. Commun. 1985 27. 132 S. P. Church F.-W. Grevels H. Hermann and K. Schaffner J. Chem. SOC.,Chem. Commun. 1985 30.133 N. Kuhn H. Schumann and G. Wolmershaiiser J. Chem. SOC.,Chem. Commun. 1985 1595. 134 C. Belin T. Makani and J. Roziere J. Chem. SOC.,Chem. Commun. 1985 118. 135 A. M. Arif A. H. Cowley N. C. Norman and M. Pakulski J. Am. Chem. SOC.,1985 107 1062. 136 H. Fisher and S. Zeuner. Z. Nuturforsch. Teil B 1985 40,954. 220 J. E. Newberry SCN-(CO),M=C(H)R -(CO),M[S=C(H)R] M = Cr W; R = -C,H,,2,4,6-C,H2Me3 or -C6H4X (X= CF,,CH,,OMe) Scheme 11 the sulphur or q2from the S=C bond. The two forms can be readily distinguished by infrared spectroscopy. For tungsten the q1form is favoured for C6H4-oMe whereas there is a q2dynamic equilibrium for C6H4-CF3 C6H4-Me and C6H5. Increasing the temperature shifts the equilibrium towards the q1form and use of hexane as solvent favours the q2 form.The structure of an alkyne ( q2)complex with tungsten has been determined,'37 (Scheme 12). The tungsten is raised above the equatorial plane with the angle Cl-W-Cl being 168". I-c-c-I ] WCl + I-C=C-I A [wc14(I-c~c-I)]* -ii Clfy$J PPh, c1 c1 c1 Reagents; i CCI,; ii PPh,CI/CH,CI Scheme 12 The use of interactive molecular graphics which is widely employed in studying protein conformations has been successfully applied138 to a study of steric con- straints in sulphido bridged materials of the form [(C5H5-,Me,)MoS(p-S)]2 n = 0 or 5. The syn form is more common but the anti form is found with some ligands including C5Me5. The graphics technique shows that the intramolecular van der Waals energies of the syn isomers are higher than the corresponding anti forms.Stereochemical factors are also used'39 in giving an explanation for the reaction between Cr(C0)6 and 3-benzoylpyrrole to give a .rr-complex rather than the u-complex formed by 2-benzoylpyrrole (Scheme 13). The molybdenum .rr-complex shown in Scheme 14 has been found14' to give an inter-metallic complex in a reaction with (Ph3PAu),0+BF in thf. The product takes up a '4-legged piano stool' format and has Mo-Au of 2.71 A. 137 K. Stahl U. Muller and K. Dehnicke 2. Anorg. Allg. Chem. 1985 527 7. 138 J. M. Newsam and T. R. Halbert Inorg. Chem. 1985 24 491. 139 N. J. Gogan J. Doull and J. Evans Can. J. Chem. 1985 63 3147. 140 B. N. Strunin K. I. Grandberg V. G. Andrianov V.N. Setkina E. G. Perevalova Yu.T. Struchkov and D. N. Kursanov Dokl. Chem. (Engl. Trans].) 1985 281 106. Ti,Zr Hf;V Nb Ta; Cr Mo W; Mn Tc Re 221 + I CH=NMe2 -aCH-NMe2 Reagent i (P~,PAu)~O+BF; Scheme 14 ti CF3 iii R = CF, '1ii,R=COh /-I I ,CF3 Reagents i MeCECMe EtzO 20 "C;ii MeO2CC-CCOZMe Et,O 20 "C;iii F,CC=CCF, Et,O 70 "C. Scheme 15 The catalytic role of these early transition metals is important in several areas of current interest. One possible route for alkyne oligomerization has been investi- gatedt4* for a number of tungsten complexes (Scheme 15). Addition of MeCECMe L. Carlton J. L. Davidson P. Ewing L. ManojloviC-Muir and K. W. Muir J. Chem. SOC.,Chem. Commun. 1985 1474. J. E. Newberry to the q2-vinyl complex [W{ 72-C(CF3)C(CF3)SR’}(CF3CeCCF3)( q5-C5H5)] gives a product (15A) quite different from that with either MeO,CC_’CCO,Me or F3CCECF3 which seem to be further stages in the formation of oligomers.The individual complexes produced are not related as though they were frozen-out steps in one process but may well represent such steps. As a final example of Group 6 organometallic compounds a series of fulvene complexes may be e~amined.’~’ If bis( 7-benzene) molybdenum (or tungsten) is treated with 6,6-dimethylfulvene or 6,6-diphenylfulvene then a fulvene molecule is able to displace one of the aryl rings. The complex formed (18) was examined by 13C n.m.r. and photoelectron spectroscopy. The bending of the exocyclic carbon towards the metal was shown directly by X-ray diffraction and both sets of spectro- scopic information had features specific to this bonding mode.5 Manganese Technetium and Rhenium There have been a number of interesting general reviews in which these metals feature and a few that deal with problems specific to Group 7. Thus a detailed review has been made’43 of the redox thermodynamics of Mn”’ and MnIV complexes. Both protic and aprotic solvents are considered and the discussion also considers the relevance to both dioxygen reactivity and biological systems. A bridge between inorganic chemistry and nuclear medicine has been constructed in a review14 of recent advances in technetium chemistry which deals with structural relationships between complexes and their application as organ-imaging agents.The topic is further developed’45 in a broader account which covers the whole area of technetium radiopharmaceuticals from the production of 99mTc through to a wide range of applications. The preparation of [Na99”TcNC14] is fairly typical of continuing efforts at expanding the range of Tc-radiopharmaceuticals. It offers a route into a whole range of nitrido complexes which in viuo experiments on mice have to possess significantly different organ distribution patterns from the corresponding 0x0-compounds. 142 J. A. Bandy V. S. B. Mtetwa K. Rout J. C. Green C. E. Davies M. L. H. Green N. J. Hazel A. Izquierdo and J. J. Martin-Polo J. Chem. SOC.,Dalton Trans. 1985 2037. 143 K. S. Yamaguchi and D. T. Sawyer Israel 1.Chem. 1985 25 164. 144 E. Deutsch and K. Libson Comments on Znorg. Chem. 1985 111 83. 145 T. C. Pinkerton C. P.Desilets D. J. Hoch M. V. Mikelsons and G. M. Wilson J. Chem. Educ. 1985 62 965. 146 J. Baldas and J. Bonnyman Znt. J. Appl. Radiat. Zsot. 1985 36 133. 147 J. Baldas and J. Bonnyman Znt. 1. Appl. Radiat. Zsot. 1985 36 919. Ti,Zr Hf;V Nb,Ta;Cr Mo,W;Mn,Tc Re With the growth in the use of whole-body scanners there is a demand for preparations that have contrast-enhancement capability. It has been claimed'48 that if manganese citrate is incorporated into phosphatidylcholine vesicles then the paramagnetism of the manganese may give useful effects in n.m.r. scanners. The material has been tested on rabbits and specific absorption noted by major organs such as liver spleen kidneys and heart.Coordination Compounds.-Treatment of TcNC~,(M~~P~P)~ with stoicheiometric proportion of S2C12 in dichloromethane at room temperature gives'49 the Tc' thio- nitrosyl complex Tc( NS)Cl,( Me2PhP)3. However if the conversion is attempted using a vast excess (20 1) of reagent under reflux then the Tc" complex is formed Tc( NS)C13( Me,PhP),. The interconversions were monitored by e.p.r. spectroscopy. Both rhenium and technetium form MCl,(py) when the complex salt (py.H),MC16 is heated to around 300 "C. Infrared spectroscopic assignments suggest'50 that a cis isomer is formed. When dinitrogen is bound to rhenium an electron-rich site is established which becomes attractive to other ligating species.Thus the complex trans-[ReCl( N2)- (diph~s)~] will react with a number of different thiolate species. The dinitrogen ligand is readily expelled and S-bonded complexes produced instead. ''' In view of the wide-ranging recognition of the biological role of manganese it is perhaps surprising that there are few known examples of complex formation with such important ligands as imidazole. Addition'52 of a 10-fold excess of imidazole (Him) to a dmf solution of the ethane-dithiolate complex [M~~~(edf)~],- gives a colour change from dark to light green. Addition of acetone allowed crystals of [Mn(edt),(Him)]-to be isolated. The manganese( 111) is in a square-pyramidal site (19) with the imidazole in the apical position. As expected the manganese is raised slightly above the basal plane (0.38 A) and the imidazole ring is planar.HC-N I1 \\ HC ,CH NH The structures of some other dithiolates have also been inve~tigated."~ Reaction of MnC12.4H,0 with Na,(tdt) in methanol where tdt is toluene dithiolate gives [Mn(tdt),].[PPh,],. If oxygen is admitted prior to the crystallization stage then the product obtained is [Mn(tdt),][ Mn(tdt),MeOH].[ PPh4I2. The first product was 148 T. Parasassi G. Bombieri F. Conti and U. Croatto Znorg. Chim.Acta 1985 106 135. 149 L. Kaden B. Lorenz R. Kirmse J. Stach and U. Abram 2. Chem 1985 25 29. 150 0. Yu. Levanda A. A. Oblova A. F. Kuzina L. I. Belyaeva and V. I. Spitsyn Russ. J. Znorg. Chem. (Engl. TrunsL) 1985 30,522. 151 A. J. L. Pombeiro and R.L. Richards Transition Met. Chem. 1985 10 463. 152 J. L. Seela J. C. Huffman and G. Christou J. Chem. Soc. Chem. Commun. 1985 58. 153 G. Henkel K. Greiwe and B. Krebs Angew. Chem. Znt. Ed. Engl. 1985 24 117. 224 J. E. Newberry shown to have Mn" in a distorted tetrahedral environment whereas the oxidized product has a Mn''' centre with a square-planar arrangement. This product has also a second anion with methanol in the apical position of a square pyramid [similar to the imidazole complex (19)]. The manganese complexes Mn( PR,)X2 where X = C1 Br or I and R3 = various combinations of Ph Bu Pr Et Me have been examined for their reactions with CS2 and SO,. With CS2 in diethyl ether a dimeric product was ~btained.'~~ It was formulated as {Mn(PR3)X2},.CS2 but there was no real evidence presented for a bridging mode being taken up by the CS2 molecule.It is clear however that the species is strongly held as the composition of the complex is resistant to heating. The ability of the phosphine complex to react with SO2 was found to be highly dependent upon the complex formulation. For X = C1 no reaction was obtained but for X = I then a complex MnX2PR2( was obtained. This was an irrever- sible complexing process which occurred also with the bromide species for all non-phenyl containing phosphines. c1 PPh3 Et I/ 0-Re-0 Ph3P'I c1 The structure (20) of ReC120(OEt)(PPh3) has been re~0rted.l~~ It is almost orthogonal in the all-trans conformation. The angle Cl-Re-C1 is 172.4" while 0-Re-0 is 179.1".Other octahedral compounds that have been investigated include K2ReF6 and [TcOC15]-. The trigonally distorted rhenium salt was studied'56 by infrared spectroscopy at room temperature and 10 K. The vibrational spectrum was assigned by using information from an analysis of the hot bands in the polarized electronic spectra at room temperature and at 120 K. The anion [TcOCl,]- which was prepared15' by the reduction of TcO by HC1 was studied by e.p.r. spectroscopy. It was not possible to obtain good quality spectra at room temperature but intense resonances typical of an axially symmetric complex were obtained at 130 K. Finally in this section on mononuclear complexes some solution chemistry will be examined. Redox parameters are for the Tc'"/Tc"' couple in aqueous bicarbonate solution.The system was studied by controlled potential coulometry at an optically transparent electrode (spectro-electrochemistry). Both states were stabilized by car- bonate and bicarbonate ions. Related work was carried'59 out with some trans-[Tc( PR,R'),L]+ mixed-ligand complexes where R,R' are Et Ph and L is a tetradentate Schiff base. Propylene I54 (a) D. S. Barratt and C. A. McAuliffe Inorg. Chim. Acta 1985,97 37; (b)D. S. Barratt C. G. Benson G. A. Gott C. A. McAuliffe and S. P. Tanner J. Chem. SOC.,Dalton Trans. 1985 2661. R. Graziani U. Casellato R. Rossi and A. Marchi J. Cryst. Spectrosc. Res. 1985 15 573. M. Bettinelli L. di Sipio A. Pasquetto G. Ingletto and A. Montenero Inorg.Chim. Acta. 1985,99 37. R. Kirmse J. Stach and U. Abram Inorg. Chem. 1985 24 2196. J. Paquette and W. E. Lawrence Can. J. Chem.. 1985 63 2369. A. Ichimura W. R. Heineman and E. Deutsch Inorg. Chem. 1985 24 2134. I55 156 157 158 159 Ti Zr Hf;V Nb Ta; Cr Mo W; Mn Tc Re 225 carbonate solutions of the complexes were investigated by spectro-electrochemistry at a gold minigrid. A reversible reduction from Tc"' to Tc" was observed and also a reversible oxidation Tc"'/Tc'~. The Eo values vary from -1.1 1 to -0.69 V for the reduction and +0.62 to +0.79V for oxidation (both us. Ag/AgCl) for the various complexes examined. The potentials are affected by the nature of both the phosphine and Schiff-base ligand.The energy of the charge-transfer bands was found to be a linear function of the redox potential Tc"'/Tc'". A different style of investigation was made for another series'60 of mixed-ligand complexes. Paramagnetic relaxation rates for both 13C and 31P n.m.r. were studied for the ternary system glycine/ Mn2+/ATP in water-glycerol solution. For the binary system Mn2+/ATP three complexes could be detected corresponding to the stepwise formation of Mn(ATP)2- Mn(ATP):- and Mn(ATP)y-. However in the ternary mixture over a similar Mn2+/ATP range only one complex Mn(ATP)(Gly)2- was found to be present. The glycine ligand is attached only through the carboxylate whereas for binary Mn2+/Gly complexes the amino-group is also coordinated. Macrocyclic ligand complexes are very important for the Group 7 metals.Two nitrido phthalocyanine species have been reported. The technetium(v) complex was vacuum sublimed for purity and characterized161 by mass spectroscopy. The rhenium(v) version was prepared162 by heating together ReOC13( PPh3)2 NH,Cl and phthalodinitrile at 300 "C for 30 min. Aspects of the electrochemistry were reported. The porphyrin complexes are mostly four-coordinate as for example [Mn"'tpp].ClO, where tpp is tetraphenylporphyrin. It is known that these can interact with a range of neutral molecules to add on two axial ligands making a six coordinate high-spin manganese d4 ion. The species [Mn(tpp)(dmf),]+ formed by the addition of dmf has been shown163 to have a very long Mn-0 bond (2.217 A). In solution there is fast exchange of the axial ligands and the geometry is found to vary between six-coordinate (predominates below -10 "C) and five-coordinate (favoured above 10 "C).The manganese porphyrins are studied primarily as models for the manganese species that occurs in photosynthetic systems. It is not clear what role this complex takes whether as a central catalyst for water oxidation or as a member of an electron-transport chain. Manganese porphyrins have the potential to 'store' redox steps and could thus be worth considering as photosynthetic sys- tem~.~~~ However the life times are rather too short for operational purposes and it is necessary to use a diamagnetic photosensitizer while the paramagnetic manganese acts as an electron receiver.Under these conditions photoreductions took place but no photooxidation. If the processes were repeated with the porphyrins incorpor- ated into a vesicle (phosphatidylglycerol) or a micelle (SDS) then reduction still occurred but at a reduced rate. None of the systems tested look really promising and perhaps it is necessary to hold the two components into some pre-arranged geometry that has been customized for efficient electron-transfer. 160 J. J. Led J. Am. Chem. SOC.,1985 107 6755. 161 S. Rumrnel N. Hermann and K. Schmidt 2. Chem 1985 25 152. 162 A. Mrwa S. Rummel and M. Starke 2. Chem. 1985 25 186. 163 C. L. Hill and M. M. Williamson Znorg. Chem. 1985 24 2836. 164 H. Ellul A. Harriman and M.-C. Richoux J. Chem. SOC.,Dalfon Trans. 1985 503.226 J. E. Newberry If TcOC1 is treated with a large excess of ethanedithiol then a rather unusual bridged complex is formed (TcO),( SCH2CH2S)3. This was studied by single-crystal X-ray diffraction and shown'65 to have each metal in a roughly square pyramidal array with the apical oxygens tightly held at Tc-0 of 1.66 8 (21). The technetiums are 0.74 and 0.80 8 above the basal planes and the two metals have an edge-sharing arrangement with an angle of 106.0' between the two sets of four sulphur atoms. Me Me2 'TJ \ CH2 c1 p' Rhenium has an extensive chemistry of metal-metal bonded complexes starting with the classic anion Re,Cl;-. If this species is reacted with any of a range of bidentate phosphines complexes such as Re2C14(LL) may be formed.'66 With the phosphine Me,P(CH,),PMe, an eclipsed configuration is adopted (22) with a metal-metal bond of 2.26A that is formally a triple bond with the a2.rr4626*2 configuration.With Ph2PCH2PPh2 the phosphine forsakes the chelate position and adopts a bridging mode which imposes a staggered configuration on the molecule to make a torsion angle of Cl-Re-Re-C1 of 56.0". The Re-Re bond length is 2.23 A. If this complex Re,Cl,(Ph,PCH,PPh,) is reacted with carbon monoxide then one or two carbonyls can be taken up.'67 The bis-complex was found to be C12Re(p-C1)(p-CO)(p-diphos)2ReC1(CO), and could be described as two edge- sharing octahedra. The Re-Re distance is 2.58 A which seems far too long for a triple bond. It could be that the core is now best described as a Re;+ moiety rather than the triple-bonded Re:+.The 13C n.m.r. spectra show a fluxional process in solution that leads to the carbonyl ligands being regarded as equivalent. The monocarbonyl complex also has fluxional properties consistent with variation between Cl,Re(p-diphos) ReC1,CO and CI,Re( p-Cl)(p-diphos),ReClCO. Organometallic Compounds-A number of different complexes of general formula MBr(C0)5-,(ER2) where E = S Se or Te and for M = Re n = 1 or 2 and for M = Mn n = 2 have been prepared.16' The kinetics of ER displacement by CO was followed and shown to be progressively slower in the order S Se Te. Rather more interestingly it was observed that when Mn(CpMe)(C0)3 is photolysed in the presence of SMe or SeMe, then it is a carbonyl group that is replaced and the bridged species (23) is formed.These were found to have similar structures differing mainly in the bridge angle of Mn-S-Mn at 125.1" and Mn-Se-Mn of 127.1'. 165 A. Davison B. V. de Panphilis R. Faggiani A. G. Jones C. J. L. Lock and C. Orvig Can. J. Chem. 1985 63 319. 166 T. J. Barder F. A. Cotton K. R. Dunbar G. L. Powell W. Schwotzer and R. A. Walton Inorg. Chem. 1985 24 2550. 167 F. A. Cotton L. M. Daniels K. R. Dunbar L. R. Favello S. M. Tetrick and R. A. Walton J. Am. Chem. Soc. 1985 107 3524. 168 A. Belforte F. Calderazzo D. Vitali and P. F. Zanazzi Gun. Chim. Ira/. 1985 115 125. 227 Ti,Zr Hf;V Nb Ta; Cr Mo W; Mn Tc Re Much of the interesting carbonyl chemistry of these metals is concerned with the dinuclear carbonyls M2(CO),, and their simple substitution products.The products of phosphine substitution such as Mn,(CO),(P(OMe),} or Re,(CO),( PMe,Ph) have been analysed by single-crystal X-ray diffraction and shown to have staggered configurations (24) with Mn-Mn 2.91 A and Re-Re 3.04 A. Apparently the substitution process has very little effect upon the M-M bond (as judged by the bond length). 0 0 c co c\ /C0 I/ (Me0)3P-Mn Mn -P(OMe)3 Some 55Mn n.m.r. spectra have been reported’71 for the series of compounds Mn,(CO),.{E(CF,),}.Y where E =P or As and Y =halogen or E’R with E’ =S Se or Te. Quite good spectra were observed with resolution of most of the ”Mn- ,‘P one-bond couplings. A wide range of chemical shifts (-415 to -1450p.p.m.relative to KMnO,) was observed. Kinetic studies have been made” on thermally induced processes in the complex Mn2(C0)8(PPh3)2. First some scrambling reactions such as the formation of Mn,(CO),( PPh,)( PBu:) from an equimolar mix of two bis-phosphine complexes in decalin were monitored by infrared spectroscopy. Some clean isobestic points were found. The reactions were unaffected by the addition of free PPh, and nor did PPh promote the formation of the mixed complex when added to a solution of the bis-PBuy complex. These observations support the view that substitution processes [e.g. by CO or P(OPh),] proceed via spontaneous homolysis of the Mn-Mn bond. The photoelectron (HeI HeII) spectra of a number of complexes with 7-bound ligands have been rep01ted.l~~ The complexes M( q5-CsH7)(CO), M( T~-C,H,M~)- (CO), M( ~5-CSH7)(CO)2P(OMe)3 and Mn( q3-CSH7)(C0),PMe3 where M =Mn or Re were studied.For the manganese versions of the first two species the spectra were virtually unchanged from that obtained for MnCp(CO),. There were obvious alterations in the ligand peaks but the effect on the metal ionization seemed to be very small. A molecular orbital scheme to account for the observations was presented. 169 H. Masuda T. Taga T. Sowa T. Kawamura and T. Yonezawa Inorg. Chim. Acta 1985 101 45. 170 G. W. Harris J. C. A. Boeyens and N. J. Coville J. Chern. SOC.,Dalton Trans. 1985 2277. 171 J. Grobe J. Vetter and D. Rehder Z. Natutforsch. Teil B 1985 40,975. 172 A. Poe and C. V. Sekhar J.Am. Chem. SOC.,1985 107 4874. 173 J. C. Green M. de 10s Angeles Paz-Sandoval and P. Powell J. Chem. Soc. Dalton Trans. 1985 2677. J. E. Newberry Co-condensation of rhenium atoms fails to give a product with either benzene or cycloheptatriene. However co-condensation with an equimolar mixture of the organics gave'74 two red air-sensitive mixed-ligand complexes (25) in roughly equal quantities. The compound Re( q6-C6H6)( T~-C~H,) (25A) could be obtained free of the other species by chromatography on alumina. However it was not possible to obtain pure samples of Re( T6-c6H6)( q5-C7H9) (25B). The substances were charac- terized by application of 2D n.m.r. spectroscopy which enabled all the coupling constants to be assigned and the C-C connectivity to be elucidated.Bis(neopenty1) manganese Mn( Me3CCH2)2 is believed to be a linear Mn alkyl- bridged tetramer in the solid state although the details have never been published. It is known to sublime readily and has been studied in the gas-phase at 140°C by electron diffraction. The radial distribution curve shows no sign of the presence of anything but a monomer and the structure (26) has been proposed. This has a central C-Mn-C angle of 180" and a torsion angle between the two groups of 160". Me\LMe Me /L\ I /CH2-Mn-CH2 Me C /\ Me. 'Me Treatment of (~~-c~Me~)Re0~ by excess PPh3 in aerated thf gave'76 a yellow to brown colour change and the deposition after 20min of blue-green crystals of empirical formula (C5Me5)3Re5014.This was found to be a 2 :1 electrolyte with two ReO ions and gave a very simple 'H n.m.r. signal of only one line. The cation was shown by single-crystal X-ray diffraction analysis to be [( q5-C5Me5)3Re3(p-O),12+ (27). The six bridging oxygens can be placed at the corners of a trigonal prism with 174 M. L. H. Green and D. O'Hare J. Chem. SOC.,Chem. Commun. 1985 332. 175 R. A. Anderson A. Haaland K. Rypdal and H. V. Volden J. Chem. SOC.,Chem. Commun. 1985 1807. 176 W. A. Henmann R. Serrano M. L. Ziegler H. fisterer and B. Nuber Angew. Chem. Int. Ed. Engl. 1985 24 50. Ti,Zr Hf;V Nb Ta; Cr Mo W; Mn Tc Re the rheniums occupying a capping position on each rectangular face. The Re-Re distances average out at 2.75 A not disimilar from double bonds.An alternative description of the structure is of a trimeric edge-sharing square-planar (LReO,) complex. Finally a number of tetranuclear metal clusters have been synthesized’” by reacting Co,(CO) with ReM( rCC6H,-Me-4)(CO) in hydrocarbon solvents. Examples with M = Cr Mo or W were prepared and the structure determined for the tungsten variant (28). It is notable that none of the carbonyls occupies a bridging mode. When heated to ca. 100 “C a dicobaltrhenium complex is formed which was found to be [Co2Re(~~-CC6H4-Me-4)(co)~~] (29). This contains the first character- ized Co-Re bond (mean length of 2.70 A) and again has no bridging carbonyls. 177 J. C. Jeffery D. B. Lewis G. E. Lewis and F. G. A. Stone J. Chem. Soc. Dalton Trans. 1985 2001.