Ti Zr Hf; V Nb Ta; Cr,Mo W; Mn Tc Re By J. E. NEWBERY Department of Chemistry University of London Goldsmiths’ College New Cross London SE 14 6NW 1 Introduction Section 7 attempts to present some of the more interesting and important pieces of work published on the chemistry of the early transition metals. One of the fascinating aspects of review work is the sudden appearance of a whole new area of development. Such a situation arose in the late 70s when the chemistry of metal-metal bonds really underwent expansion with publications rapidly increasing from the rate of ca. 20 per annum to the current level of around 100. A good readable chronicle of this area has recently been presented.’ 2 Titanium Zirconium and Hafnium A photoelectron spectroscopic investigation into ZrH,,, ZrXH0.5 and ZrXH (X = C1 or Br) has indicated substantial Zr-H covalency,2 and that no major differentiation should be made between the nature of hydrides and that of other binary compounds.The zirconium monohalides ZrCl and ZrBr have novel layered structures with a stacking sequence X-Zr-Zr-X. Reaction between the halide and Zr02 has been shown3 to follow the equation ZrX + nZrO = ZrXO,. + nZrO with x and y up to about 0.4. The basic crystal framework is unchanged by this reaction and the oxygens are randomly distributed between the zirconium layers. The monohalides were also shown to be resistant to intercalation of small molecules. Cs2TiC1,.4H20 has been shown4 by single-crystal X-ray diffraction analysis to contain tr~ns-[TiCl~(H~O)~]+ ions.The compound has an ill-defined shoulder in the electronic spectrum at 10 K which may be indicative of this trans configuration. A series of titanium P-diketonate complexes has been studied’ by n.m.r. spectros- copy. For the complexes shown in (l) with R = Pri Bu’,-CH,Ph or -C(Me),Ph and R’ = Me or But the rates and activation parameters both for inversion and R’ exchange were determined. The values obtained were shown to be almost indepen- dent of both complex concentration and the solvent. They were also similar for the two processes indicating a common intramolecular mechanism. The ratio between ’ F. A. Cotton J. Chem. Educ. 1983 60 713. J. D. Corbett and H. S. Marek Inorg. Chem. 1983 22 3194. L. M. Seaverson and J. D. Corbett Znorg.Chem. 1983 22 3202. P. J. McCarthy and M. F. Richardson Inorg. Chem. 1983 22 2979. ’ R.C. Fay and A. F. Lindmark J. Am. Chem. Soc. 1983 105,2118. 171 J. E. Newbery R' H 0'qRt RO..,.. I .,o .Ti>''. RO' R' H (1) the two rate constants (ki,,/kexch) falls from -2.0 to -1.0 as the steric bulk of the alkyl groups increases. In [RB(pz),]Zr(OBu')Cl, where pz = pyrazoyl the zirconium atom is in an octahedral site being co-ordinated by a nitrogen from each of the pyrazoyl rings. For R = H pz Pri or Bun the complexes are fluxional6 at room temperature but for R = H and with the 3,5-dimethylpyrazoylborate,a 2 1 pattern is shown in both 'H and 13C n.m.r. spectra as a result of the differing environments. Kinetic processes in Group IV octaco-ordinate complexes have also' been investi- gated by n.m.r.The N,N-dimethylmonothiocarbamate (Me,NCSO-= L) complexes ML4 M = Ti or Zr have AG* of cu. 75 kJmol-' for C-N rotation and cu. 45 kJ mol-' for metal-centred rearrangement. The corresponding dithiocarbamates (R,NCS,) are still non-rigid on the n.m.r. time-scale at -140 "C. The range of ligand types found with Group IV metals is quite large. In Zr(BH,Me), the metal has been shown' by X-ray diffraction to have the expected tetrahedral co-ordination from the boron atoms (Zr-B = 2.56 A) but also to be in close proximity to the BH protons. Phosphine ligands however are generally regarded as being more difficult to co-ordinate. The ligand N(SiMe,CH,PMe,), (L) has the advantage of having a 'hard' amido centre to act as an anchor-point and yet might still involve 'soft' phosphorus.Reaction of Li.L with either ZrC14 or HfC14 gives MC12L2 and a single-crystal X-ray diffraction study' has shown distor- ted-octahedral geometry with one phosphorus atom free and the other co-ordinated. The porphyrin complex Ti(OMe)tpp where tpp is tetraphenylporphyrin is noteworthy" for having the methoxy group almost coilinear with the metal (Ti-0-Me = 171") and a rather short Ti-0 bond (1.77 A). Some of the more interesting organometallic species reported for this group involve various metallacycles. A useful new route to the metallacyclobutanes has been described" (Scheme 1). The method also should be effective with other metals. The synthesis of oxa-metallacycles has been shown' to result from using an alkoxide to promote ring closure (Scheme 2).The structure has been confirmed by X-ray analysis and has the two bent metallocenes linked by two oxygen bridges. D. L. Reger and M. E. Tarquini Inorg. Chem. 1983 22 1064. ' S. L. Hawthorne A. H. Bruder and R. C. Fay Inorg. Chem. 1983 22 3368. R. Shinomoto E. Gamp N. M. Edelstein D. H. Templeton and A. Zalkin Inorg. Chem. 1983,22,2351. M. D. Fryzuk H. D. Williams and S. J. Rettig Inorg. Chem. 1983 22 863. C. J. Boreham G. Buisson E. Duke J. Jordanov J.-M. Latour and J.-C. Marchon Inorg. Chirn. Actn 1983 70 77. 'I J. W. F. L. Seetz G. Schat 0. S. Akkerman and F. Bickelhaupt Angew. Chem. lnt. Ed. Engl. 1983 22 248. I* H. Takaya M. Yamakawa and K.Mashima 1. Chem. SOC.,Chem. Commun. 1983 1283. '0 Ti,Zr Hf;V Nb Ta; Cr Mo W;Mn,Tc Re Me Me CpMCI, Mg ~ Mze21 MfiMe Et,O Br Br BrMg MgBr -Et,O ' M cp' 'cp M = Ti Zr or Hf Scheme 1 R n\ R = H or Me \ K Scheme 2 Et Et-CZC-Et - Cp2Mp-(I CP 2M Et M = Ti or Zr Scheme 3 Various metallacyclopentadienes are shown13 (Scheme 3) to undergo ring expansion with alkynes into metallacycloheptatrienes. The products were identified by their mass spectra and from the nature of the hydrocarbons formed on treatment with HC1-CHCl,. The lability of the carbonyl groups in Cp,Ti(CO) is well-estab- lished,I4 and they have now" been shown to be capable of replacement by S4N4 giving Cp2Ti(N4S3). The titanium atom is bonded to two nitroogens to form a metallathiazene ring.The (NS)atoms are almost planar (k0.12 A) with the metal 0.58 A above the ring. Some five-co-ordinate metallocene complexes have been characterized. (Cp),Zr(CF,SO,),.thf has been shown16 to have Zr-0-S at 155.2' and the angle betweep the two rings at 127.8". The Zr-0 distance to the thf is significantly longer (2.278 A) than that to the OS02-CF3 group (2.219 A). In (Cp),ZrCl(S,CNEt,) the Cp rings make a similar angle of 128.9' at the metal centre." The Zr C1 and two S atoms of the bidentate ligand lie in a quasi mirror-planeFlmost peTendicular to the plane of the Zr and the centroids of the Cp rings. At 2.56 A and 2.72 A respectively the Zr-C1 and Zr-S distances are exceptionally long. A Cp-Zr-Cp angle of 128.8" also is found'* in one of the products of the reaction of diazoalkanes R,C=N=N (R = Ph or CO,Et) on Cp,ZrRi (R' = Me or CH2Ph) or (Cp,ZrHCl),.An insertion process into the Zr-C or Zr-H bond l3 A. Famili M. F. Farona and S. Thanedar J Chem. SOC.,Chem. Commun. 1983 435. l4 B. H. Edwards R. D. Rogers D. J. Sikora J. L. Atwood and M. D. Rausch J. Am. Chern. SOC.,1983 105 416. C. G. Marcellus R. T.Oakley A. W. Cordes and W.T. Pennington J. Chem. Soc. Chem. Commun. 1983 1451. l6 U. Thewalt and W. Lasser 2.Naturforsch. Ted B,1983 38 1501. " M. E. Silver 0. Eisenstein and R. C. Fay Inorg. Chem. 1983 22 759. l8 S. Gambarotta C. Floriani A. Chiesa-Villa and C. Guastini Inorg. Chem. 1983 22 2029. J. E. Newbery occurs with the formation of a q2-N,N hydrazonato ligan! (2).The nitrogen carrying the R' group is the closer of the two (Zr-N = 2.lOA and 2.28A). q2-N,N is in~olved'~ also in the reaction product of azo compounds R-N=N-R (R = Ph or p-MeC,H,) with Cp2Ti(C0),. The metal atom is shown to take up pseudo- tetrahedral co-ordination with the angle Cp-Ti-Cp being 133.0". The N-N bond distance is 1.34 A and the nitrogen atoms are at 1.965 and 1.971 A from the metal. Results from a quantitative ab initio molecular orbital treatment of TiCl,(MeN=NMe) as a model are consistent with the conformation adopted. Me \ Ph\ N cp ,C," \ I Zr -Me Ph I CP (2) The formation of a number of zirconium(rI1) hydrides and alkyls is reported. Reduction of ZrCp2C12 by Mg-thf gave" a reddish-brown coloration with the presence of a Zr"' paramagnetic species being revealed by the intense e.s.r.spectrum obtained. Initially a singlet flanked by 9'Zr satellites was observed but over a period of 48 hours this turned into a doublet. Detailed analysis of the spectra and of others from reductions in the presence of substrates such as styrene indicates the formation of a mononuclear zirconium(Ir1) hydride. The hydrogen appears to have been abstracted from a Cp ring. Hydrides are also postulated2' as products from the photolysis of ZrCp,RX and ZrCp,X,. When carried out in the presence of phos- phines a different e.s.r. signal was obtained suggesting the formation of tertiary phosphine adducts of Zr"'. The compound Ti(q-C7H7)(q-C7H9) is normally produced by the reaction of T~(T-C~H~M~)~ with cycloheptatriene in the presence of (A1Et2Cl), resulting in near quantitative conversion.If however the titanium starting material is treated with (AlEtCl,) and cycloheptatriene in tetrahydrofuran red crystals of a binuclear complex are obtained.22 The structure [Ti( q-C7H7)(C,H,0)(fi-Cl)]2 was elucidated by X-ray diffraction methods. The dichloro bridge can be cleaved by tertiary phosphines or amines and species of the type Ti( q-C,H,)(t-ph~s)~Cl formed. Further treatment with Grignard reagents allowed compounds such as (3) to be synthesized. The X-ray-determined structure gives no indication of interaction between the metal and ethyl group hydrogen atoms. (3) l9 G. Fochi C. Floriani J. C.J. Bart and G. Giunchi 1. Chem. Soc. Dalton Trans. 1983 1515. 20 E. Samuel Inorg. Chem. 1983 22 2967. *' A. Hudson M. F. Lappert and R. Pichon J. Chem. Soc. Chem. Commun. 1983 374. 22 M. L. H. Green N. J. Hazel P. D. Grebenik V. S. B. Mtetwa and K. Rout J. Chem. SOC.,Chem. Commun. 1983 356. Ti,Zr Hf;V Nb Ta; Cr Mo W; Mn,Tc Re Finally in this section on Group IV transition metals there are some reports on heterobimetallic complexes. Thus M(CO),(Cp) (M = Ti or Zr) will react23 with W( rCC6H4Me-p)(CO),(Cp) in toluene to give MW(p-CC6H4Me-p)(p-CO)(CO) (CP)~. The structure of the titanium fpecies was determined by X-ray diffraction (4). The Ti-W bond length is 2.977 A. The bridge system is nearly linear and the W-carbonyl group q2to the titanium makes a decidedly non-linear angle (OCW = 165").One interesting point is that although their environments are quite distinct C H Me l6 c? .F+ /"" TI-W c; 1 c' 'CP (.j4 (4) only one resonance was observed for the 13C0 n.m.r. at room temperature for the Zr complex. Two peaks differing by only 0.6 p.p.m. were seen on cooling to -80 "C. Similar behaviour was also observed24 for the complex Cp2RZr- RU(CO)~C~ with R = Me. With R = OCMe3 the Zr-Ru distance in these unbridged entities was shown to be 2.91 A. 3 Vanadium Niobium and Tantalum LiV2F6 has been shown25 to be a true mixed-valance compound. It exhibits a trirutile lattice with two edge-sharing distorted VF6 octahedra and a single V site. The complex compounds will be classified in the order mononuclear bridged and metal-metal bonded moieties.The polymeric entity {V(NO),Cl2}, can26 be reduced by Na/Hg in acetonitrile. In the presence of ligands complexes such as V(N0)2L2Cl(L = MeCN or methyl isonicotinate) or [V(NO),(BU'NC)~]PF~ can be isolated. The compounds were characterized by infrared analysis and from "V n.m.r. The oxovanadium ion V02+ exhibits a strong preference for oxygen donors when offered2' the compartmental ligand derived from (5). Whereas both copper(I1) and (5) 23 G. M. Dawkins M. Green K. A. Mead J.-Y. Salaun F. G. A. Stone and P. Woodward J. Chem. Soc. Dalton Trans. 1983 527. 24 C. P. Casey R.F. Jordan and A. L. Rheingold J. Am. Chem. SOC.,1983 105 665. 2s R. M. Metzger N. E. Heimer C. S. Kuo,R.F. Williamson and W.0. J. Boo Inorg. Chem. 1983 22 1060. 26 M. Herberhold and H. Trampisch Inorg. Chim. Acta 1983 70 143. 27 J.-P.Costes and D. E. Fenton J. Chem. SOC.,Dalton Trans. 1983 2235. J. E. Newbery nickel(I1) give a mixture of two complexes showing either all oxygen or oxy-gen/nitrogen donation to the metal V02+ gives only the former. Heterocyclic amines (L) have been known to co-ordinate to vanadium(I1). A more convenient route to such species as VL4X2 or [VL6]X2 X = C1 or Br is28 uia the ethanolate. Mixture of the hydrated vanadium dihalide with ethanol and triethyl- orthoformate gives VBr2.6EtOH or VCl,.n EtOH (n = 4 or 2). These are exceptionally useful as sources of V"' in cases where water may oxidize the potential ligating molecule.In a similar vein the structures of VC13.3thf and VC12.2thf are reported.29 While the former is monomeric mer-VCl,(thf), based on octahedral co-ordination (angles are cis Cl-V-Cl of 92.0" and cis 0-V-0 of 86.2"),the latter complex is shown to be not even a pure vanadium compound since it is actually [V2(p- Cl),(thf)&[Zn,(p -C1)2C14]2-. Apart from the vanadium (and of course zinc) the analytical percentages are similar for the two formulations. The structure of the cation is based on face-sharing of two regular octahedra. A 1 1 reaction product is readily formed from NbSC13 and Ph3PS. This has now been established3' by X-ray crystallographic work to consist of two separate species. Each unit-cell contains two monomer units and one dimer.The monomers are five-co-ordinate square pyramidal with the lone sulphur atom occupying the axial position. The metal is displaced towards this atom (above the square plane) by 0.55 A. The dimeric unit contains edge-sharing distorted octahedra (6). ,s /\ I CI PPh (6) The vapour-phase decomposition of a number of fluorinated V'"0 /3 -diketones shows3' the formation of VOF2 and a furanone (e.g. C5HF,02 C5H4FZ02 etc.). A correlation has been noted32 between both the frequency and the extinction coefficient and the solvent strength (defined in donor/acceptor terms) for the elec- tronic absorption spectrum of VO(acetylacetonate) in fifteen different organic solvents. The synthesis of a number of novel vanadium(v) alkoxides is reported.33 VO(0R) (dipic).H,O (where dipic is 2,6-pyridinedicarboxylate)and VO(OOR)(dipic).H20 were prepared from aqueous solution by standard procedures.The structure of the latter species with R = But is notable for the presence of an 0-0-bonded 2n L. F. Larkworthy and M. W. O'Donoghue Inorg. Chim. Acra 1983 71. 81. 29 F. A. Cotton S. A. Duraj M. W. Extine G. E. Lewis W. J. Roth C. D. Schrnulbach and W. Schwotzer J. Chem. SOC.,Chem. Commun. 1983 1377. 30 M. G. B. Drew and R. J. Hobson Inorg. Chim. Acm 1983 72 233. 3' D. A. Johnson and A. B. Waugh Polyhedron 1983 2 1323. 32 A. Urbanczyk and M. K. Kalinowski Monatsh. Chem. 1983 114 13 I I. 33 H. Mimoun P. Chaumette M. Mignard L. Saussine J. Fischer and R. Weiss J. Nouu. Chim. 1983 7 467. Ti,Zr Hf;V Nb Ta;Cr Mo W;Mn Tc Re alkylperoxo group (7).oThe terminal oxygen being closer to the metal (1.87 A) than the latter group (2.00A).The angle 0-V-0 is 43.4'. Such structures may prove to be common amongst dn metal alkylperoxo intermediates involved in the catalytic epoxidation of olefins. Q (7) In the general trend towards the elucidation of the biological role of vanadium several reports of complex formation involving ligands of potential biological significance have appeared. Purine or adenine (L) can co-ordinate to vanadium(1v) to produce3 VO(LH)C12. Vanadium(II1) forms green water-soluble complexes with the amino acids methionine glutamic acid and aspartic acid.35 Both simple (e.g. V glu V asp, or V met,) and mixed ligand (e.g. V asp.met V asp.glu or V glu.met) examples were characterized by thermal analysis and infrared spectroscopy.With cysteine vanadium(r1) rapidly forms36 a complex V" cys. Over a period of a few minutes this decomposes to the corresponding V"' species with the evolution of dihydrogen. Hydrogen release is suppressed by the addition of either V'" or cystine but V"' cys is still formed. Thiolate bonding analogous to that involved in cysteine linkages is found in the complexes formed from the ethane- 1,2-dithiolate ion (edt). VO(acac) will give3' the ion [V0(edt),l2- while VC13 produ~ed~'*~* [V,(edt),12-. The former ion is found to be square pyramidal with the oxygen taking the apical position. The V-0 distance is 1.62 A and thus a little long for such (V=02') moieties and perhaps explains the lowish V-0 stretching frequency at 928 cm-'.Analysis of the e.s.r. spectrum indicates that there is enhanced electron density at the metal as compared to that found for VO(acac),. In the ion [V2(edt),I2- the structure found corresponds to [(edt)V(p-edt),V(edt)I2-where each vanadium is in a sevtrely distorted octahedral environment. There is also a possible V-V bond (2.60 A). An interesting effect is in the complexes TaCl,(diph~s)~ and [TaCl,(diphos),]+ where diphos = Me,PCH,CH2PMe2. The neutral molecule adopts a square anti-prismatic structure with Ta-Cl = 2.50 A and Ta-P = 2;65 A whilst the comelex ion is dodecahedra1 with the Ta-Cl bond length of 2.43 A and Ta-P of 2.69 A. It is well-established that these structures are of similar stability and it thus becomes difficult to ascribe a reason for the switch.Dodecahedra1 co-ordination is also ~uggested~"~' in the preliminary reports of the X-ray structures on the hydride complexes TaCl,H,(diphos) and TaCl2H,(PMe3),. 34 C. M. Mikulski S. Cocco N. de Franco and N. M. Karayannis Inorg. Chim. Acta 1983 78 L25. 35 1. Grecu R. Sandelescu and M. Nearntu Andes de Quimicu 1983 79 18. 36 G. Kalatzis J. Konstantatos E. Vrachnou-Astra and D. Katakis J. Am. Chem. SOC.,1983 105 2897. 37 R. W. Wiggins J. C. Huffman and G. Christou J. Chem. SOC.,Chem. Commun. 1983 1313. 38 (a) J. R. Dorfrnan and R. H. Holm Inorg. Chem. 1983 22 3179; (b) D. Szeymies B. Krebs and G. Henkel Angew. Chem. Int. Ed. Engl. 1983 22 885. 39 F. A. Cotton L.R. Falvello and R. C. Najjar Inorg. Chem. 1983 22 770. 40 M. L. Luetkens jun. J. C. Huffman and A. P. Sattelberger 1. Am. Chem. Soc. 1983 105 4474. 4' M. L. Luetkens jun. W. L. Elcesser J. C. Huffman and A. P. Sattelberger J. Chem. Soc. Chem. Commun.. 1983. 1072. 178 J. E. Newbery Turning to macrocyclic ligands the niobium(rv) porphyrins NbX,(por) where (por) = tetraphenyl- tetra-rn-tolyl- or tetra-p-tolyl-porphinato can be conveniently synthesi~ed~~ from the corresponding NbvX,(por) species (X = CI or Br) by reduc- tion with zinc amalgam. Irreversible oxygenation readily occurs and causes the appearance of a new e.s.r. line the structure of which is in accord with the formation of a superoxo NbV complex NbX,O,(por). Analysis of EXAFS data supports axial symmetry for a series of compounds VIVS(por) formed from V"(por)(thf) by direct action of sulphur.43 An unusual dinuclear vanadate complex is formed by the reaction between VC1,.3thf and 2-hydroxy-6-methylpyridine (HL) to give44 V202C1,(p-HL),.This has apparently neutral molecules in a bridging role but actually employs the zwitterion form 2-0x0-6-methylpyridinium. The N-H protons were located in the X-ray crystallographic analysis. Two of the bridging ligands are asymmetrical and one is symmetrical. The metals are in a very distorted octahedral environment with the V-V distance quite large at 3.175 A. E.s.r. evidence was used to show the presence of oxovanadate(1v) rather than (v). The addition of diphenylethyne to a mixture of NbCls and NbOCl in dichloromethane dark green crystals of formulation (C,ClPh,)+( Nb20C19)-.X-Ray crystallographic analysis shows the presence of this interesting oxygen-bridged dinuclear dimer (Nb-0-Nb = 174.1") but surprisingly enough the dimer is also associated via unsymmetric chloro bridges into a centrosym- metric tetramer (8). This bridge has equal Nb-Cl separation within each arm but a considerable difference between the arms (249 pm and 270 pm). NBut c1/ 6'.1 Cl\\ /Cl c1,Nb\ c1I c1 I NBut The reaction between V(NPh)Cl and Bu'(Me,Si)NH produces a product that has been identified46 by X-ray analysis as having the structure (9) V,Cl,(NBu'),(p,- NPh),(p,-PhNCONHBu'). This has a (VN) ring with the metal bridged by pheny- limido groups at fairly uniform distances (V-N = 1.85 to 1.9 I A).Each vanadium is at the centre of a distorted trigonal bipyramid. The most interesting part of the structure is the formation of the PhNCONHBu' ligand which then adopts a triple- bridging mode via the oxygen atom. 42 P. Richard and R. Guilard J. Chern. SOC.,Chern. Cornmun. 1983 1454. 43 J.-L. Poncet R. Guilard P. Friant and J. Goulon Polyhedron 1983 2 417. 44 F. A. Cotton G. E. Lewis and G. N. Mott Znorg. Chern. 1983 22 378. 4s E. Hey F. Weller and K. Dehnicke Z. Anorg. Allg. Chern. 1983 502 45. 46 D. C. Bradley M. B. Hursthouse A. N. de M. Jelfs and R. L. Short Polyhedron 1983 2 849. 179 Ti,Zr Hf;V Nb Ta; Cr Mo W;Mn Tc Re S4N4 reacts4' with VC14 in dichloromethane to give a mixture of VC12(S2N3) and S2N2VC14.The latter compound proved to be difficult to obtain in a completely pure form but the former crystallizes into black needles. It was shown to consist of chloro-bridged dimers further linked into a polymeric chain (10). (10) Metal-metal bonds are present in quite a few Ta"' dinuclear complexes. Ta,C16(Me2PC2H4PMe2)2 is formed4' from Ta,Cl,(Me,S) as red crystals by the direct action of the diphosphine in dichloromethane solution. It has two bridging chlorines in an edge-sharing mode between two octahedrons with the phosphorus atoms all in equatorial positions. This is a distinct difference from the related Ta2Cl6(PMe3) complex where one paireof phosphines are equatorial and the other are axial. The Ta-Ta distance is 2.71 A consistent with a double bond.A minor by-product of the reaction (1 l) has a further arrangement of the diph~sphines.~~ Ta,Cl,(diphos),(p -O)(p-SMe,) is evidently formed by traces of water in the reaction mixture and may have a (p-OH) group instead of the 0x0 group protons being rather d$€icult to locate. This is also a Ta=Ta complex with an inter-metal distance of 2.73 A. ON (1 1) (12) Vanadium shows a single V-V bond (2.61 A) in the compound (Pr'Cp),V2S4 prepared5' from (Pr'Cp)VC12. The metals are bridged by one 7'-S2 ligand and by two S ligands. The former ligand is converted into the v2-S2bridging mode by reaction with hexafluoro-but-2-yne to give the black lustrous (Pr'Cp)V2S4.C2(CF3)2 where the butyne has added across the single sulphides to form a p-v2-S2C2(CF3) ligand.A related vanadium compound (MeCp),V2S4 reacts5' with Hg[Fe( NO) (CO)3]2 in toluene to give a molecule with a cubane structure (MeCp),V,Fe,( NO)& (12). The species is electron-deficient (58e) Fnd shows some signs of intermetallic contact (Fe-Fe = 2.59 A Fe-V = 2.75 A and V-V = 2.95 A). A linear heterometallic complex ion [VFe2S4Cl4I3- can5* be precipitated from an acetonitrile solution containing [FeCl,]- and [VS,]'-by the addition of ether. 47 H. W. Roesky J. Anhaus H. G. Schmidt G. M. Sheldrick and M. Noltemeyer J. Chem. SOC.,Dalron Trans. 1983 1207. 48 F. A. Cotton L. R. Falvello and R. C. Najjar Inorg. Chem. 1983 22 375. 49 F. A. Cotton and W. J. Roth Inorg. Chem. 1983 22 868. 50 C. M.Bolinger T. B. Rauchfuss and A. L. Rheingold J. Am. Chem. Soc. 1983 105 6321. 5' T.B. Rauchfuss T. D. Weatherill S. R. Wilson and J. P. Zebrowski J. Am. Chem. Soc. 1983 105,6508. 52 Y.Do E. D. Simhon and R. H. Holm 1.Am. Chem. SOC.,1983 105 6731. J. E. Newbeiy The absorption spectrum of this ion in acetonitrile is recognizable as that of a perturbed [VS,]'- chromophore. The solid-state structure has ifealized D2d sym-metry about the vanadium (13) and the V-Fe distance of 2.73 A is similar to that in the cubane (12). (13) (14) The structure of 'VCl,(thf),' has been shown29 to be [v,(p-C1)3(thf)6]2[zn&16]. If a thf slurry of this species is mixed with PMe2Ph followed by LiBH an actual heterometallic complex is formed. V,Zn2H,(BH,)2(PMe2Ph)4 has been shown53 to be symmetrical about a central V-V structure (14).Organometallic Compounds.-V(CO) is the only homoleptic metal carbonyl that is a stable free radical. In the solid state it appears black as a result of a weak electronic transition centred at 580 nm. In dilute solution or at 15 K in a nitrogen matrix it shows no absorption below ca. 840nm. Based on SCF-Xa-DV calculations it is suggested5 that the solid-state transitions show some analogy to donor-acceptor charge-transfer bonds with the process v(co),v(co) -?+~V~C~),'.l[V(CO),l becoming important. The "V n.m.r. spectra of a series of complexes [V(CO),L]- have been measured.55 The chemical shifts from the various ions were arranged in a series that reflects decreasing T-and increasing cT-interaction as the electronegativity of L increases CO > CNR = SbR > PR > AsR > BiR > DMSO (S-co-ordinated) > NCR > py > (oxygen donors) The chemical shifts relative to VOC13 ranged from -1951 p.p.m.for L = CO to -534 p.p.m. for L = 02NPh. The thermally unstable and highly reactive molecule V(CO)5N0 has been known for a number of years but there is little information on its reactions. It can be readily obtained in high yield by mixing [Et,N][V(CO),] and [NO][BF4] in dichloromethane. A large number of reactions was investigated (Scheme 4).56 Two facile syntheses are reported for M(C0); (M = Na or Tb). Starting from MCl, the complex M(C,,H,)2- was first formed5' by addition of sodium naph- thalenide in DME. This complex ion takes up carbon monoxide quite readily at -60 "C and atmospheric pressure to yield M(C0);.Alternatively the chloride can be turned into M(C0); by reductive carbonylation with Mg-Zn-py-CO. 53 R. L. Bansemer J. C. Huffman and K. G. Caulton J. Am. Chem. SOC.,1983 105 6163. 54 G. F. Holland M. C. Manning D. E. Ellis and W. C. Trogler J. Am. Chem. Soc. 1983 105 2308. 55 D. Rehder and K. Ihmels Znorg. Chim. Acfa 1983 76 L313. 56 K. L. Fjare and J. E. Ellis J. Am. Cbem. Soc. 1983 105 2303. 57 C. G. Dewey J. E. Ellis K. L. Fjare K. M. F'fahl and G. F. P. Warnock Organornernllics 1983 2 388. 58 F. Calderazzo U. Englert G. Pampaloni G. Pelizzi and R. Zamboni Inorg. Cbem. 1983 22 1865. Ti,Zr Hf;V Nb Ta; Cr Mo W;Mn Tc,Re V(CO),( NO)(diphos) (i) Na(DME)Cp [CO) MnV( CO),NO]- [V(CO),NO],( diphos) [v(co>4(No)II-trans-V(CO),(NO)(NMe,) tmns-V(CO),( NO)( PR,) Scheme 4 For niobium the process works at room temperature and atmospheric pressure with ca.48% yield. The ion is capable of further reduction59 by sodium in liquid ammonia to give Na,[M(CO),J. The caesium version of this salt has the unsociable habit of being shock-sensitive and thus liable to explode. Spin-lattice relaxation methods were employed6' to show that the barrier to the rotation of the cyclopentadienyl ring in CpV(CO) is 7.1 kJ mol-*. An interesting series of nobium complexes where the metal progresses from do to d2 has been prepared.61 [NbR,(Cp),]+ [NbR2(Cp),J and [N~R,(CP)~]- where R = (o-CH&H,)~ were produced in forms suitable for single-crystal X-ray analysis.In very broad terms the niobium is tetrahedrally bonded but there are progressive changes for example the torsion angle of the biphenyl changes from 59.6" to 62.4" and finally to 78.4". The angle CH2-Nb-CH2 alters from 80.0"to 83.0" and 106.3". The full structural characterization of a T8-C8H8 vanadium complex is reported.62 (q8-C8H8)V[Et2C2B4H4]was synthesized by the reaction of K2C8H8 with [2,3- (Et)2C2B4H5]- and VC13 in tetrahydrofuran. It was isolated as a dark green air-stable solid after t.1.c. separation using hexane as eluant. X-Ray crystallographic analysis shows a sandwich environment for the metal (15). The vanadium atom is 1.375 A from the C8 plane and 1.830 A from the C2B3 ring of the carborane.4 Chromium Molybdenum and Tungsten A number of reviews concerning Group VIB metals have been published. These are mostly concerned with the biological role of the elements. Thus chromium can be 59 G. F. P. Warnock J. Sprague K. L. Fjare and J. E. Ellis J. Am. Chem. SOC.,1983 105 672. 60 D. F. R. Gilson G. Gomez I. S. Butler and P. J. Fitzpatrick Can. J. Chem. 1983 61,737. 6' L. M. Engelhardt W.-P. Leung C. L. Raston,and A. H. White J. Chem. SOC.,Chem. Commun. 1983,386. 62 R. G. Swisher E. Sinn G. A. Brewer and R. N. Grimes J. Am. Chem. Soc. 1983 105 2079. 182 J. E. Newbery classed63 as an ultra-trace element essential to animal life. In the natural state it is found as Cr"' but 'man-made' CrIVis carcinogenic.Model compounds that attempt to mimic aspects of the Mo-hydroxylases are reviewed64 in an account with 67 references. For convenience the rest of this section will be subdivided into 'simple' compounds co-ordination compounds and organometallics. Simple Compounds.-This designation covers both binary compounds and some complex ions particularly the heteropolyanions. The structure of NaMO,O is chain-like based on trans edge-sharing octahedra. A one-dimensional model has been developed65 to discuss the metal-metal interac- tions in such extended systems. Although having seemingly obvious limitations the model proved useful in many aspects of the chemistry of this class of compounds particularly in suggesting that structural distortions result from increasing the elec- tron count on the molybdenum chains.Possible structures (16) for a number of molybdenum ions in aqueous solution are suggested from Fourier transform analysis of EXAFS data.66 Lf I+ MoV Mo'" .-2.54H-+ L+ Mo'" The preparation and unit-cell parameters of a number of complex salts A,[MOX,] where A = K Rb or Cs; M = Cr Mo or W; and X = C1 or Br are With potassium only K,MoOCI could be isolated and this may result from excessive solubility of the other salts. Gaseous chromyl fluoride Cr02F2 has been investigated by electron diffraction procedures.68 A quadratic force-field waszvaluated and force constants determined by normal co-ordiKate analysis. The F-Cr-F angle was found to be 111.9" larger than that of 0-Cr-0 (107.8') but not an excessive deviation from tetrahedral symmetry.The mixed-valence ion [W408C18(H20)4]2- can be produced by an equilibrium between Wv'02CI~- and W"0CI;- in concentrated hydrochloric acid. It does not show high stability but the corresponding thiocyanate [W408(NCS)12]6- gave a 63 W. Mertz Chem. Scr. 1983 21 145. 64 J. T. Spence Coord. Chem. Rev. 1983 48 59. 65 T. Hughbanks and R. Hoffmann J. Am. Chem. SOC.,1983 105 3528. 66 S. P. Cramer P. K. Eidem M. T. Paffett J. R. Winkler Z. Don and H. B. Gray J. Am. Chem. Soc. 1983 105 799. 67 J. E. Fergusson A. M. Greenaway and B. R. Penfold Inorg. Chim. Acta 1983 71 29. R. J. French L. Hedberg K. Hedberg G. L. Card and B. M. Johnson Inorg. Chem. 1983 22 892. Ti,Zr Hf;V Nb Ta; Cr Mo W;Mn,Tc Re caesium salt that was studied69 by X-ray crystallographic methods (17).The tungsten atoms form a regular plane and are each roughly octahedral. The disposition of the terminal oxygens differs from that found previously for the chloro ion where an alternating geometry was observed. s C S (17) Moving on to the heteropolyanions evidence is presented7' for the formation of 1 1 complexes between a number of tungsten species and polylysines. Precipitation can be induced and a reactivity order NaAs,W,,O:~ > NaSb9W2,0~~-> SiW,,O& was established. This has some similarities to in vivo and in vitro antiviral activity of these polyanions which are believed to inhibit DNA and RNA poly- merases. Polypeptide precipitation is recommended as a simpler test to apply and a correlation with electrostatic charge per accessible surface area is suggested as an explanation of the reactivity differences.Many of the interesting papers in this area now involve the application of Ig3W n.m.r. studies. For example the PWIIOi; ion can form 2 1 complexes with f-transition metals. Thus with cerium paramagnetic [Ce"'(PW 1039)2]11-and diamag- netic [Ce'"(PW 1039)2]10-can be formed.71 A sharp six-line spectrum is observed for the paramagnetic ion and a much more complex pattern for the diamagnetic. It is suggested that whereas the 'ligands' in the former ion are twisted by either 0" or 180" in the latter there is a 90" twist. A six-line spectrum was also found7* for TiPW (intensity order 2 :2 :1 :2 :2 :2).A detailed analysis of the spectrum and peak assignment was made by constructing a chemical-shift/spin-couplingmatrix. TiPW,,O:; shows five peaks of equal inten~ity.'~ For maximum utility of Ig3W n.m.r. results in these complex systems it is essential to have unambiguous peak assignment. This can be achieved7 through the use of a similar procedure to that employed for I3C,namely two-dimensional n.m.r. Several examples are quoted and contradictions with some recent assignments are evident. Some data have been obtained on ligand exchange in lacunary heteropolytung- The process studied was the expulsion of water from such anions as 69 J. P. Launay Y. Jeannin and A. Nel Inorg. Chem. 1983 22 277. 70 M. Hervi G. Hervt F. Sinoussi J.-C.Chermann and C. Jasmin Now. 1. Chim. 1983 7 515. " L. P.Kazansky and M. A. Fedotov J. Chem. Soc. Chem. Commun. 1983 417. 72 W. H. Knoth P. J. Domaille and D. C. Roe Inorg. Chem. 1983 22 198. 73 P. J. Domaille and W. H. Knoth Inorg. Chem. 1983 22 818. C. Brevard R. Schimpf G. Tourni,and C. M. Tourni. J. Am. Chem. Soc. 1983 105 7059. 74 75 F. Zonnevijlle C. M. Tourni and G. F. Tourni Inorg. Chem. 1983 22 1198. 184 J. E. Newbery [MFe(H20)W,,039]n- (where n = 4 M = P or As; n = 5 M = Si or Ge; or n = 6 M = B) and [M2Fe(H20)W,706,]7- (for M = P or As). Values of the standard equilibrium constant were obtained from spectroscopic measurements using Job’s method (continuous isomolar variation) or molar ratio variation. For Fe(CN)z- as the exchanging ligand the values found were over ten times larger than those for S20<- but much alteration was evident along the series of polyanions and also from changes in solution pH.A study has been made of the reduction characteristic^'^ at a glassy carbon electrode of a number of heteropolyanions of general formula (P2W,8-n MO,O,~)~-. The ions divide into two classes depending on whether the observed 2e-change occurs in one step or two steps. This division was correlated with changes in the M-0-M angle between the two ZM ‘half-anions’. Co-ordination Compounds.-The classification followed in this section starts with mononuclear compounds and moves via bridged complexes through to metal-metal bonded entities. Within each sub-group the articles are arranged by donor type and in order of increasing ligand denticity.The formation and reaction of dinitrogen complexes continues to produce some exciting results. One preliminary note7’ records the possible formation of a bis carbon dioxide complex for molybdenum by the loss of dinitrogen from Mo(N2) (Ph2PCH2CH2PPh2). This was achieved by direct action as a yellow air-stable compound in 75% yield. The complex tran~-Mo(N~)~(triphos)(PPh,) is known to decompose with evolution of ammonia on treatment with HBr-thf. On a closer e~amination’~ the initial formation of hydrazine can be detected. This was attained by allowing the decomposi- tion to run for a set time then removing volatiles and adding water-CH2C12 to the solution. Analysis of the aqueous phase was then made to detect the amounts of hydrazine and ammonia present.The hydrazine yield goes through a maximum of ca. 0.16 mol N2H4 per mol Mo after about one hour and then progressively decreases. The ammonia yield continually rises being ca. 0.15 mol per mol Mo after 1 hour and 0.72 mol per mol Mo after 60 hours. The production of hydrazine in this fashion is similar to the behaviour found in nitrogenase. Mixtures of trans-Mo(N,),(PMePh,) and pyridine (or 4-Me py) eq~ilibrate’~ with rrunqrner-Mo(N2),(py)(PMePh2) and the equilibrium constants have been found by 31P n.m.r. to be four and seven (for py and 4-Me py respectively). If a five-fold excess of the tetra-phosphine complex is added this trans,mer complex can be precipitated but as a mixture.Benzene solutions of the complex are purple and decompose in vacuo depositing red-brown precipitates. These have been shown by n.m.r. spectroscopic methods to be formulated as .rr-complexes Mo(~,~,-py) (PMePh,),. In this area of study much attention has been directed at trans-M~(N~)~(phos)~ species and thus the synthesis characterization and an account of some of the properties of a cis variant is very welcome.8o cis-[Mo(N,),(PMe,),] was prepared 76 J. P. Ciabrini R. Contant and J. M. Fruchart Polyhedron 1983 2 1229. 77 J. Chatt W. Hussain and G. J. Leigh Transition Met. Chem. 1983 8 383. 78 T. A. George and L. M. Koczon J. Am. Chem. Soc. 1983 105 6334. 79 R. H. Morris and J. M. Ressner J. Chem. SOC.,Chem. Commun.1983 909. 80 E. Carmona J. M. Martin M. L. Poveda J. L. Atwood and R. D. Rogers J. Am. Chem. SOC.,1983 105 3014. Ti,Zr Hf;V Nb Ta; Cr Mo W; Mn Tc Re according to (Scheme 5) by reduction of a Mo"' complex. Also noteworthy is the reaction product with further PMe3 where one of the dinitrogens has been expelled to give Mo(N~)(PM~~)~. Crystallographic structural data are reported" for two molybdenum-nitrogen complexes. MoN(N,)(diphos) is octahedral about the metal with equatorial phos- phines. The azide group is of special interest in being linear (N-N-N = 179"). The Mo-N (nitrido) is rather long at 1.79 A and this may result from the trans azido-group. A similar overall geom:try was found also in [MoBr(NH)(diphos),]+ where the Mo-Br distance is 2.61 A and Mo-NH is 1.73 A.Preparative procedures for the synthesiss2 of a range of organoimido-tungsten compounds are shown (Scheme 6). These complexes are notable for having tungsten tin oxidation states IV v and VI.X-Ray structural data were obtained on a number of these compounds. Perhaps the most interesting of these is the W'" species W(NPh)Cl,(PMe,),. This has rner-phosphines and each of the phosphines is cis to the -NPh group. WOCl [W(NR)C13L; rW(NR)CI L31 L' = PMe,Ph PPh (L = PMe, PMe,Ph or CNBu') L; = Ph2PCH,CH,PPh2 Reagents i RNCO; ii MgMe + PMe,; iii Na/Hg; iv thf Scheme 6 Arylamido molybdenum complexes can be prepared from a dichloromethane solution of [Mo{HB(M~,~z)~}(NO)I~], where Me,pz = 3,5-dimethylpyrazolyl by addition of the appropriate arylamine.A series of such complexes of general formula " J. R. Dilworth P. L. Dahlstrom J. R. Hyde and J. Zubieta Inorg. Chim. Acta 1983 71 21. D. C. Bradley M. B. Hursthouse K. M. A. Malik A. J. Nielson and R. L. Short J. Chem. SOC.,Dalton Trans. 1983 2651. 186 J. E. Newbery [Mo{HB(Me2pz),)(NO)I(NHR)] where R = phenyl and various substituted phenyls has been characterized spectroscopically.83 No connection could be deter- mined between the v(N0) and the nature of the phenyl substituent. The NH protons appear in the 'H n.m.r. as sharp singlets (6 = 11.14-13.15 p.p.m.) and do not exchange with D20. Compounds of similar formulation but involving hydrazido ligands have also been synthesi~ed.~~ [Mo{HB(Me2pz),}(NO)I(NHNRRf)] shows octahedral geometry about the molybdenum for R = R' = Me and R = Me R' = Ph with a fac boron-ligand (a triple N-donor).The -NHNRR' group is unidentate in both cases with Mo-N-N = 140.3' and 144" respectively. A sealed-tube reaction between (*)-cis-[Cr(en),FCl]I and dry liquid ammonia gives rise to [Cr(en),FNH,]ICI in a cis-truns ratio of 4 1. This ratio was determined by h.p.l.~.~' The presence of trans product indicates that a trigonal bipyramidal complex is a likely intermediate. The polymeric [MO(NO)~CI~], can be used86 as a starting material for the produc- tion in dichloromethane solution of a range of neutral complexes Mo(NO),L2C12 (where L = MeCN PhCN PPh3 or py; L2 = bipy or diphos). The bipyridyl com- plex [Mo(NO),bipyCl,] has been studied by X-ray crystallography and shows an approximate octahedral arrangement with cis-dinitrosyls and trans-dichloros.The nitrosyls are roughly linear (175.9" and 177.4'). The chloro groups in this class of compounds can be displaced by stirring in 1,2-dimethoxyethane (dme) to yield8' the cations [Mo(NO),L,(dme)CI]+ and [Mo(NO),L2(dme),12+. Some of these have proven active as catalysts for the polymerization of norbornadiene. A rather fascinating bipyridyl complex formulated M~~Cl,(bipy)~ is produced" by direct action on Mo2C14(p-C1)2(p-H9C4-C~C-C4H9)(OPC13)2. An X-ray structural investigation showed that the action of the bipyridyl cleaves all the bridging units in the original complex to form a complex salt [cis-MoC12(bipy),]'[MoC1,(bipy)]- where both ions are octahedral.Formulations such as that make it quite hard to appreciate the mode of attachment in complexes such as Cr3L5C14.2H20 (L = purine or adenine).89 MoC1 will react with thiazylchloride to give a product" CI,Mo=N=SCl which is likely to be a dimer. Addition of POC13 produces a complex Cl,PO.Mo(Cl),NSCI and further treatment with chloride ion will give a complex anion [Cl,MoNSCI]-. An interesting series of simple mononuclear nitrosyl complexes of molybdenum has been prepared." Some data were obtained on their redox chemistry and the solid-state structures elucidated by X-ray diffraction. All showed a roughly linear disposition for M-N-0. As expected from their compositions mostly these were octahedral complexes but even so there were some points of interest.For example 83 J. A. McCleverty G. Denti S. J. Reynolds A. S. Drane N. El Mum A. E. Rae N. A. Bailey H. Adams and J. M. A. Smith 1. Chem. SOL Dalton Trans. 1983 81. 84 J. A. McCleverty A. E. Rae I. Wolochowicz N. A. Bailey and J. M. A. Smith 1,Chern. SOC.,Dalton Trans. 1983 71. 85 J. W. Vaughn Inorg. Chem. 1983 22 844. 86 D. Ballivet-Tkatchenko C. Bremard F. Abraham and G. Nowogrocki 1. Chem. Soc. Dalton Trans. 1983 1137. a7 D. Ballivet-Tkatchenko and C. Bremard 1. Chem. SOC.,Dalton Trans. 1983 1143. 88 E. Hey F. Weller B. Simon G. Becker and K. Dehnicke Z. Anorg. Allg. Chem. 1983 501 61. 89 C. M. Mikulski S. Cocco N. de Franco and N. M. Karayannis Inorg. Chim. Am 1983 80 L71. 90 U. Kynast and K.Dehnicke Z. Anorg. Allg. Chem. 1983 502 29. 9' A. Muller W. Eltzner S. Sarkar H. Bogge P. J. Aymonino N. Mohan U. Seyer and P. Subramanian 2. Anorg. Allg. Chem. 1983 503 22. Ti,Zr Hf;V Nb Ta; Cr Mo W;Mn Tc Re 187 while [Mo(NO),(NCS),]'- and [Mo(NO)(H,O)C~,]~- are octahedral [Mo(NO) (H2N0)(NCS),]'-adopts a pentagonal bipyramidal configuration. In the preparation of related nitrosyl complexes x was never greater9* than 1.5 in MO(NO)~CI~(ROH) for a range of monofunctional alcohols. To achieve the co-ordination of two alcohol functions a diol was necessary e.g. [MO(NO)~C~~((CH~OH)~}]. Papers concerning oxygen-donor ligands and Group VI transition metals seem much less prevalent than those of either nitrogen- or sulphur-donors. Crown ethers do appear capable of stabilizing the rather elusive CrV oxidation state.If non-aqueous reduction of K2Cr207 is performed93 in the presence of 18-crown-6 Cr" is the most stable species generated. This was deduced from e.p.r. measurements. Cr" formation constants with a wide range of ligand types have been measured9 by potentiometric procedures. Ammonia ethylenediamine diaminopropane malonate glycinate p-alaninate iminodiacetate nitrilotriacetate and ethy-lenediaminetetra-acetate ligands were chosen for study. There were several dis- crepancies found from various previous compilations of data for Cr". In the present case the values obtained are compared to those of Cu'+ after taking account of the difference in ionic radii of the metals. As mentioned at the start of this section on Group VI transition metals naturally occurring chromium is found as Cr"'.Brewer's yeast contains chromium and the complexing entity could be either amino acids or nicotinic acid (3-carboxypyridine or niacin HL). Carboxylate binding is certainly very strong with this ligand-metal-ion combination and the solid-state structure of [Cr(HL)2(NH3)4](C104)3.2H20showsg5 it to have doubly protonated trans-pyridiniumcarboxylate groups. Each carboxylate acts in a monodentate fashion. The angle across the centre (0-Cr-0) is virtually linear (172.0'). Complete separation of the A and A isomers of Cr(a~ac)~ was achieved96 by h.p.1.c. methods in ca. 15 minutes. A chiral packing material (+)-poly(triphenylmethy1 methacrylate) was used and the best separation was attained by using 80% methanol-20% water as the eluting solvent.The range of complexes utilising sulphur donation is certainly much wider than that of oxygen. A number of different MoIV complexes involving S-bonded ligands has been prepared and their i.r. 13C n.m.r. and charge-transfer spectra mea~ured.~' Evidence is obtained for extensive formation of covalent bonds for example amongst the eight-co-ordinate dithio acid complexes of MoIV. Very efficient mixing of metal- ligand orbitals is probable since it was observed that the d-d transitions are buried under the charge-transfer bands n-back-bonding is also present. MoCl,(thf)z is a useful starting point for the synthesis of sulphur donor com- plexes. For example the sterically hindered thiol ligand (SC,H,Pr',)- as a sodium salt will react98 with it under a carbon monoxide atmosphere to produce [Mo(CO)~(SC~H~P~',),]-.The i.r. spectrum showed a single band in the v(C0) region at 1830 cm-I and is consistent with a trigonal bipyramidal structure having 92 L. Bencze J. Kohan and B. Mohai Acta Chim. Acad. Sci. Hung., 1983 113 183. 93 M. Mitewa P. Russev P. R. Bontchev K. Kabassanov and A. Malinovski Inorg. Chim. Acta 1983 70 179. 94 K. Micskei F. Debreczeni and I. Nagypal J. Chem. Soc. Dalton Trans. 1983 1335. 95 J. C. Chang L. E. Gerdom N. C. Baenziger and H. M. Goff Inorg. Chem. 1983 22 1739. 96 Y. Okamoto S. Honda E. Yashima and H. Yuki Chem. Lerr. 1983 1221. 97 J. Selbin Inorg. Chim. Acta 1983 71 201. 98 J.R. Dilworth J. Hutchinson and J. A. Zubieta A Chem. SOC.,Chem. Commun. 1983. 1034. J. E. Newbery the carbonyls in the axial position. This has been confirmed by X-ray crystallography. The structure shows two of the ligands in an endo configuration to one of the carbonyls and the other ligand ex0 to the same carbonyl hence reducing the steric clash from having three endo-groups. Another reaction of MoCl,(thf) is with 99 the tetradentate dithiol/thioether (LH,) to produce the complex MoCl,(L) (1 8) as dark violet crystals. A bridged species LMo(S),MoL can be produced on further reaction with sodium sulphide. (18) (19) An even more exotic ligand can be generated from the introduction of dimethyl-2- butyndioate to MoSZ- in warm acetonitrile.'" The sulphide anion has the structure {(S,),MOS}~- and reaction with the carboxyethyne opens up the S rings to produce the trigonal prismatic species [Mo{S~C~(CO,M~)~},]~- shown in (19) with only one of the ligands in full format.The s6 co-ordination polyhedron shows only minor discrepancies from D3,,symmetry with a mean S-Mo-S interligand trans angle of I35". A useful synthetic route to the MoIV dithiocarbamates (L-) MoL complexes has been published."' It is suggested that oxidative decarboxylation of Mo(CO) pro- duces high yields of the Mo'" species. Corresponding MoV' compounds are pentagonal bipyramidal; in [MoO(S,CNR,)J+ two of the dithiocarbamates are equatorial and the third has one axial sulphur and the other equatorial. The original assignment of this structure (R = Et) was for the solid state.With R = Me Et or Pr' the I3Cn.m.r. spectra have now1' been recorded and all are consistent with the structure being retained in solution. The presence of the Mo-0 anisotrophy helps in the assignment of resonances. The seeming preference of Group VI transition metals for sulphur is perhaps nowhere more important than in the attempts to establish the role of molybdenum in nitrogenase. As part of this effort a series of sulphur-donor/phosphorus-donor complexes have been prepared.lo3 The complexes [MoX2( S2CNR2)2(phos)2] where X = C1 or Br; R = Me, Et, or (CH,),; and (phos) = PPh,Me PMe2Ph PEt2Ph or i(Ph2PCH2CH2PPh2) were prepared from the MoOX2(S,CNR2) dithiocarbamate complex by direct action of the phosphorus ligand in thf.These are air-stable but 99 B. B. Kaul and D. Sellmann 2.Naturjorsch. Teil B 1983 38 562. loo M. Draganjac and D. Coucouvanis J. Am. Chem. Soc. 1983 105 139. I01 R. Lozano E. Alarcon A. L. Doadrio M. C. Rarnirez and A. Doadrio Anales de Quimica 1983,79,41. I02 C. G. Young,J. A. Broomhead and C. J. Boreham J. Chem. Soc. Dalron Trans. 1983 2135. I03 J. R. Dilworth B. D. Neaves C. J. Pickett J. Chatt and J. A. Zubieta Inorg. Chem. 1983 22 3524. Ti,Zr Hf;V Nb Ta;Cr Mo W;Mn,Tc Re can be reduced by t-phosphines in methanol to give cationic complexes [MOX(S~CNR~)~(~~OS)~]-, which although paramagnetic are e.p.r.-silent. X-Ray crystallographic analysis of two of these cations indicates pentagonal bipyramidal structures In both cases the dithiocarbamates are equatorial.The occupancy of the axial positions depends upon the nature of the phosphines. The chelating diphosphine is attached at one axial position and one equatorial whereas the bis(monophosphine) case has both phosphines in axial positions and an equatorial chlorine. Controlled potential electrolysis of such cationic species is a 2e process and under CO a species [Mo(CO)(S,CNR,),(diphos)] can be isolated. No evidence for similar N2 binding could be observed. Rather special dithiocarbamates can be obtained by incorporating the alkyl substituents and the nitrogen into one entity for example as pyrolle-N-carbodithionate (pdc). Reaction of MoCl with K(pdc) yields'04 a dark blue crystal- line solid that shows no i.r.band corresponding to Mo-0. Analysis shows it to be Mo(pdc) and X-ray diffraction data confirm the eight-co-ordinate structure. Such stoicheiometry is not unusual; what makes this compound unique is the mode of preparation. Under similar conditions most other S2CNR2 ligands would have produced a complex based on an Mo203core. The aryl dithiocarbamates seem able to stabilize the lower metallic oxidation states. Starting from Mo(CO),(pdc) it is possible to replacelo5 the carbonyls with alkynes to yield Mo(R'C,R),(pdc),. An alternative path starting from [Mo(CO),I]- where the previous carbonyl complex was not actually isolated is also described. These alkyne complexes are roughly octahedral with two bidentate (pdc) groups and two cis-parallel alkynes.'HN.m.r. spectra were taken at different temperatures and evidence obtained for two distinct fluxional processes. The rotation about the C-N bond (in the ligand) has AG' = 45 kJ mol-I and rotation of the alkynes (around the molybdenum-alkyne bond axis) has AG* = 57 kJ mol-'. Some complexes containing 0-,N- and S-donation have been described.lo6 The molybdo-oxaziridines (20) are prepared from reacting Mo02(S2CNEt2) with RsNHOH. A le reduction process was found in acetonitrile solutions and the observed potential appears to correlate with the Hammett parameters of the sub- stituent X. A further use for the dioxomolybdenum dialkyldithiocarbamate species used above is to react itio7 with an alkyl dithiocarbazate {NH,NHC(S)SR'}. The S\R' S4 N -SR' (20) X = H Me or CI R.D. Bereman D. M. Baird C. T. Vance J. Hutchinson and J. Zubieta Inorg. Chern. 1983 22 2316. I05 R. S. Herrick S. J. Nieter Burgmayer and J. L. Templeton Inorg. Chem. 1983 22 3275. I06 P. Ghosh P. Bandyopadhyay and A. Chakravorty J. Chern. SOC.,Dalton Trans. 1983 401. I07 R. Mattes and H. Scholand Angew. Chem. Int. Ed. Engl. 1983 22 245. 190 J. E. Newbery product obtained has the formulation [Mo{ N2C( S)SR'){NH,NC( S)SR'){S,CNR2)2] and a pentagonal bipyramidal co-ordination framework (2 1). The axial diazenido group is virtually linear (Mo-N-N = 178") and with Mo-N = 177 pm and N-N of 121 pm must have a considerable degree of electron delocalization. Finally amongst the sulphur-donor mononuclear complexes it is worth recording the synthesis and structural characterization of an all-sulphur donor compound [Mo{S,P(OMe),),].This was prepared'" by the addition of (NH4)S,P(OMe)2 to the Mo"' reduction product obtained from tin-reduction of MoCl,(thf),. 4 pseudo-octahedral environment was observed with the Mo-S distance ca. 2.51 A. Most of the halogen-donor complexes are dealt with under other headings and perhaps the only point of interest this year is the sugge~tion'~~ that an ill-defined shoulder in the electronic spectra of trans-dihalogen complexes is indicative of that orientation. This was noted particularly for trans-Cr(en)F,(H,O),. The shoulder is absent in trans-diaquo and trans-halogenoaquo complexes. The Group VI transition metals form an extensive range of complexes with macrocyclic ligands with most current interest centred on porphyrin adducts.The synthesis of nitrido(tetra-p-tolyIporphinato)chromium(v) is reported by two different groups. ' If hypochlorite oxidation of Cr(OH)(ttp).2H20 in a two-phase mixture of CH2C1,-NH3(aq) is allowed to proceed until the colour changes from green to red (ca. 4 h) the organic layer will contain the nitrido complex in 55% yield; the complex CrN(octaethy1porph) was prepared in a like manner.'" A similar yield was obtained' l1 for a photochemical reaction on Cr(ttp)N in methylene chloride (18 h reaction time) but the yield rose to 82% usingobenzene as a solvent. As expected the chromium was found to be slightly (0.42A) above the average plane of the pyrolle nitrogens.The Pitrido-chromium distance is consistent with that expected for a triple bond (1.56 A). MoVO(tpp)Br will react with the superoxide ion 05,to give MoiVO(tpp). If the reaction is carried out at -72 "C an intermediate complex can be recognized,'12 and evidence is presented to support the formulation of this stage as a dioxygen complex. This evidence comes partly from an examination of the e.s.r. spectra at different temperatures since if the intermediate is [Mo'"O(tpp)O,]- it will be diamagnetic and e.s.r.-silent. This was observed at -80 "C but raising the temperature allowed the lines from MoV to reappear and then eventually to decay as the final (diamagnetic) complex MoTVO( tpp) was generated. Mo'~porphyrins are often bridged species such as the [M~'~Cl(tpp)],.O complex which has each molybdenum displaced out of the plane and towards the bridging oxygen.' l3 Bridged Compounds.-The classification within this section is based around the nature of the bridging entity; obviously some appear under other headings but those included here are bridged compounds of special interest.Io8 J. R. Dilworth and J. A. Zubieta J. Chem. Soc. Dalton Trans. 1983 397. I09 J. W. Vaughn J. Cryst. Spectrosc. Res. 1983 13 231. 110 J. W. Buchler C. Dreher K.-L. Lay A. Raap and K. Gersonde Inorg. Chem. 1983 22 879. Ill J. T. Groves T. Takahashi and W. M. Butler Inorg. Chem. 1983 22 884. 112 T. Imamura K. Hasegawa and M. Fujimoto Chem. Lett. 1983 705. I I3 J. Colin B.Chewier A. De Cian and R. Weiss Angew. Chem. Int. Ed. Engf. 1983 22 247. Ti,Zr Hf;V Nb Ta; Cr Mo W;Mn,Tc Re m The molecule Cp(CO)2W(NNMe)Cr(CO)s for example has been shown to have an N,N'-bridging diazo ligand,'I4 (22). The angle W-N-N is almost linear (174.4') but Cr-N-N is at 122.3'. One feature ofthis molecule is that although the structural parameters about the chromium are entirely typical for Cr(CO),L those of the tungsten centre seem to be altered significantly by the presence of another metal. Nitrogen-bridging by phenylimido groups is shown"5 in the dimer { W(NBu') (~-NP~)C~,(BU'NH~)}~. This has rather unsymmetrically situated phenylimido groups and is notable for the hydrogen-bonding type of interaction involving two of the chlorides (23).CP I H Crystals suitable for X-ray diffraction analysis were obtained from {(p-OH) Cr(NH3)4}2.(S206)2 by an interesting technique.' l6 Taking the corresponding bromide dimer a hydrobromic acid solution was covered in gel made from a 'standard preparation available in any Danish grocery store'. When the gel was almost set a saturated solution of Na2S206 was poured over and after two days in the dark suitable crystals were obtained. The compound is clearly rather diverse since at least five different modifications were recognized each with a separate X-ray powder pattern. The geometry about each metal is roughly octahedral with cis-hydroxo bridges and four terminal ammines. Oxygen-based bridges seem to be very common in molybdenum chemistry and there are reports involving a wide range of ligating types.The compound Mo,O,.(dmso) exists as infinite chains of Mo-0 polyhedra. It can be produced by work-up of Mo03.H20 in dimethylsulphoxide.'" It has two types of molybdenum environments a tetrahedral and an octahedral. These are then linked in repeating units as (-oct-tet-oct-oct-tet-oct-),. The Mo-0-Mo angle between two octahe- dral sites is 175.3' whereas between oct-tet it is 156.7". Two other variations of Mo03(dmso). with x = 1 or 2 were also identified by thermogravimetric analysis and probably consist of all octahedral and of (oct-tet) , respectively. The dinuclear molybdenum(v) glycinate complex M~,O,(gly)~( H20)2,has been shown'" to be stable in solution (>pH 5.5) for at least 24 h.Cyclic voltammograms were used to detect the presence of a dimeric MoV-MoV' species which displays I14 G. L. Hillhouse B. L. Haymore S. A. Bistram and W. A. Herrmann Inorg. Chem. 1983 22 314. I5 D. C. Bradley R. J. Errington M. B. Hursthouse A. J. Nielson and R. L. Short Polyhedron 1983,2,843. I16 S. J. Cline D. J. Hodgson S. Kallesoe S. Larsen and E. Pedersen Znorg. Chem. 1983 22 637. I I7 E. M. McCarron 111 and R. L. Harlow I J. Chem. Soc. Chem. Commun. 1983 90. I I8 M. Chaudhury J. Chem. SOC.,Dalton Trans. 1983 857. J. E. Newbery an electronic absorption band at 850nm. Efforts to isolate this entity have so far proved unsuccessful. A single 0x0-bridge between two octahedral molybdenums normally gives a virtual linear Mo-0-Mo angle.It is probable"' that it is the presence of rather bulky groups that is responsible for the angle of 171.0' found in [{MoHB(Me2Pz)3(No)I},01. A series of complexes involving various derivatives of 8-quinolinol (LL) with general formula (LL)2.Mo203S has been described.12' 1.r. spectroscopy was used to identify the presence of Mo=O and from other spectroscopic trends plus the rather low value for the magnetic moment it is suggested that these substances are dimeric with a p-0,p-S linkage. [Mo,( NO),(S,),( S,) (0H)l3- was obtained'" after prolonged reaction between {Mo(NO)}~+ complexes and Si-. It has an unusual structure (24) where if the centre bridging atom is included the Mo-S5- Mo-S ring has crown-like orienta- tions very similar to cyclo-octasulphur.The molybdenum atoms are roughly pen- tagonal bipyramidal. (24) (25) MOOS:-reacts'22 with FeCl and sulphur (S,) in dimethylformamide to produce the anionic complex [C12FeS2MoOS2]2- which has been characterized by X-ray structural analysis and a variety of spectroscopic procedures. It has the structure shown in (25) with two p-sulphido ligands. The "Fe Mossbauer spectrum is characteristic for Fe" high-spin tetrahedral complexes formed from ligands with strong acceptor properties. Reacti01-1'~~ between [CpMo(CO),J and Zn(S3CPh)2 forms two molybdenum complexes involving the dithiobenzoate ligand a monomeric complex CpMo(CO),(S,CPh) and a dimer {CpMo(S)S,CPh},. The structure of the latter species has been investigated by single-crystal X-ray crystallography and shown to belong to a new structural class for Mo'".It has a disulphido bridge and the S,CPh' groups are each bidentate to one metal. Finally in this section on bridged species there are a large number of papers involving MS groups in what could be described as a ligating mode to another metal. These are arranged in ascending order of ligand number. One reason for the popularity of these studies is the range of thiomolybdates that are found in bioinor- ganic studies. For example a recent study has suggested that the thiomolybdate I19 H. Adams N. A. Bailey G. Denti J. A. McCleverty J. M. A. Smith and A. Wtodarczyk J. Chern. Soc. Dalton Trans. 1983 2287. I20 R. Lozano J. Roman E. Alarcon A. L. Doadrio and A. Doadrio Lopez Anales de Quimica 1983 79 187.121 A. Miiller W. Eltzner H. Bogge and E. Krickemeyer Angew. Chem. Znt. Ed. EngL 1983 22 884. 122 A. Miiller S. Sarkar H. Bogge R. Jostes A. Trautwein and U. Lauer Angew. Chem. hi. Ed. Engl. 1983 22 561. 123 W. K. Miller R. C. Haltiwanger M. C. VanDerveer and M. Rakowski DuBois Inorg. Chem. 1983.22 2973. Ti Zr Hf;V Nb Ta; Cr Mo W;Mn Tc Re species present in rumen is more likely124 to be MoSi- than MOOS;-. The anion [MoS~(CUX)~]~-= C1 or Br) can be prepared by admixture of MoSZ- and CuX (X in the correct stoicheiometric ratio in acetone solution.'25 This represents the largest metal-uptake so far recorded for a cluster species based on MoS$- and may be important in aspects of copper antagonism in ruminants.The anion is polymeric based on the unit shown in (26). Four copper atoms are bound to each edge of the MoS~core. The Cu(p2-Br)Cu bridges alternate along the cbain between two types. One involves four bonds of similar length (2.50 * 0.05 A) while the other has significant differences (2.33 2.93 2.33 and 2.79 A).Thus the ion is best described as a dimer of the [MoS4(CuBr),J2- unit. Br I cu Many of these type of anions appear as dark-red or even black and this is probably a result of sulphur + metal charge-transfer bands,'26 red-shifted from those of the parent MoS:-ion.'*' When MSZ- ions act as ligands to a five-co-ordinate metal site they are normally attached cis to the basal plane of a square pyramid. In the complex S2W(p- S)2W(NNMe2)2.PPh3 however it is probably'28 the presence of the strong .rr-bonding ligands that gives a trigonal bipyramidal arrangement about the tungsten with the hydrazido groups in equatorial sites.The WSf group is thus forced to span axial and equatorial positions and is consequently somewhat distorted (W-p-S of 2.40 and 2.53 A for example). The expected chain structure with all the metals in tetrahedral sites is observed'29 for [S2W(p-S)2Fe(p-S)2WS2J3-. The bridges are very uniform and there is a ca. 9" bend along the spine of the anion. Considerable charge delocalization from the iron is observed from analysis of the iron Mossbauer spectrum. The corresponding molybdenum species has been synthesized and it possesses an e.p.r. spectrum similar to that of the Mo-Fe protein in nitrogenase.The ultimate chic in thiometallates of Group VI is undoubtedly amongst the cubane-like structures which have a core of alternate metal and sulphur atoms arranged in a rather distorted cuboid. I24 T. T. El-Gallad C. F. Mills I. Bremner and R. Summers J. Znorg. Biochem. 1983 18 323. IZ5 J. R. Nicholson A. C. Flood C. D. Garner and W. Clegg J. Chem. Soc. Chem. Commun. 1983 1179. 126 R. J. H. Clark T. J. Dines and G. P. Proud J. Chem. SOC.,Dalton Trans. 1983 2299. 127 S. R. Acott C. D. Garner J. R. Nicholson and W. Clegg J. Chem. Soc. Dalton Trans. 1983 713. IZ8 J. R. Dilworth R. L. Richards P. Dahlstrom J. Hutchinson S. Kumar and J. Zubieta J. Chem. SOC. Dalton Trans. 1983 1489. I29 J. W. McDonald G.D. Friesen W. E. Newton A. Muller W. Hellmann U. Schimanski A. Trautwein and U. Bender Znorg. Chim. Acta 1983 76 L297. I3O G. D. Friesen J. W. McDonald W. E. Newton W. B. Euler and B. M. Hoffman Inorg. Chem. 1983 22 2202. 194 J. E. Newbery The reaction between [Mo(NC6H,Me)(p3-S)(s2P(OEt),)] and S2CN(Pr') was found13* to give a mixture of yellow and red crystals. By correct choice of recrystalliz- ation solvents it proved possible to isolate pure samples of each. The yellow compound is a dimer [Mo(NC6H,Me)(p-S)(S2CN(Pr'),)l and the red is a tetramer having the same empirical formula. The structures of these are shown in (27) and several features are essentially identical between the two examples (e.g. angles Mo-S-Mo and S-Mo-S and distances Mo-N and Mo-S).The main difference comes in the Mo-Mo separation which lengthens to 2.88 in the tetramer from 2.81 A in the dimer. R R;NC/S\Mo/S\Ma=S~~NR; 's' I 's' I NR NR S -M0- 'I NR (27) Four cubane species of formula {Cu,MS,Cl}(PPh,),(E) where M = Mo or W and E = 0 or S have been shown to be isomorph~us.~~~ The core of {Cu,MS,Cl} has each copper co-ordinated by a phosphine and the S (or 0)attached to the Mo (or W). These can thus be regarded as complexes formed by MSZ-ligands. A classification is presented' 33 of various interrelationships in structures and reactivities for clusters containing the grouping {MoFe,S,}. Various pseudo-substrate ligands that are good (T donors and/or 7~ acids were used to examine patterns in binding at cubane surfaces.Fluxionality of the clusters depends on the lability of the Mo-L binding. In the cluster [MoFe,S,(SPh)3(diallylcatecholate)L]2-*3~ the binding affinity order at the molybdenum site is RS-< PEt < CN-. The core {M2Fe2S4} is also possible and can be produced'34 for M = Cr or Mo by irradiating in thf solution as shown in Scheme 7. Evidence for this transformation is mainly spectroscopic based on mass spectrometry ' H n.m.r. and i.r. spectroscopy. Molybdenum K-edge extended X-ray absorption fine structure (EXAFS) analysis is the main tool used in identifying some of these cubane systems with active centres that are found in nitrogenases. A number of these model compounds were compared with MoFe nitrogenase protein.135 In general shape the best agreement between the Fourier transforms was found for [C1,FeS,MoS2FeC1,]*- but there was a gross mismatch in terms of peak intensity.[M~,Fe,s,(sEt),]~- a double cubane gave a reasonable intensity match but was less convincing on peak shape. Matching peaks obtained from EXAFS could well be a rather tricky occupation. A technique for fine adjustment based on models (FABM) has been des~ribed',~ to improve the 131 K. L. Wall K. Folting J. C. Huffman and R. A. D. Wentworth Inorg. Cfiem. 1983 2366. 132 A. Muller H. Bogge and U. Schimanski Inorg. Chem. Acta 1983 69 5. 133 R. E. Palermo and R. H. Holm J. Am. Chem. SOC.,1983 105 4310. 134 H. Brunner H. Kauermann and J. Wachter Angew. Chem. In&. Ed. Engl 1983 22 549. 135 B.-K.Teo M. R. Antonio D. Coucouvanis E. D. Simhon and P. P. Stremple J. Am. Chem. SOC.,1983 105 5767. 13' B.-K. Teo M. R. Antonio and B. A. Averill J. Am. Chem. SOC.,1983 105 3751. Ti,Zr Hf;V Nb Ta;Cr Mo W;Mn Tc Re S\ either Me,C,-CCr-/p'Cr-C,Me5 or "Cp' Scheme 7 comparative nature of these measurements. Correctly applied it is shown capable of determining Mo-S data (interatomic distances and co-ordination numbers) to at least 10% accuracy. Results from EXAFS will remain model-dependent unless they are established by reference to a model of proven suitability. The cubane [M02Fe&i+,]3- (L = SCH2CH,0H) catalyses the controlled poten- tial reduction of N3 and hydrazine to ammonia 1377138with the concomitant evolution of hydrogen.Hydrogen evolution occurs also from dimethylacetamide solutions of the reduced clusters [M~~Fe,s~(sPh),]~-'~- and benzenethiol. 139Absorbance changes (AA) during this evolution were found to fit best the equation AA480 = c,[PhSH] + C,[P~SH]~/*~'/~ where c1 and c2 are constants and t is the time. Taking account of the behaviour of the (4-) and (5-) anions a kinetic rate equation based on a common intermediate (Im)was developed d[H,]/dt = k[I,][PhSH]. Metal-Metal Bonded Compounds.-Reactivity in the alkoxides of tungsten and molybdenum forms the basis of a recent review.'40 There are over 90 references to these compounds with specific relevance to M-M and M-C bonding. The various types of reaction are related to the structural mores of the alkoxides.Generalized molecular orbital and configuration interaction calculations have been performed on a progression of diatomic molecules and on Mo~H,.'~' The derived potential energy curve shows a minimum at a realistic value of 2.194 A and the dissociation energy is estimated as 284 kJ mol-I (MorMo). For the molecule Mo2(NH& a value of 401 kJ mol-' is obtained. The increased bond strength reflects the .rr-donation ability of -NH2. I37 Y. Imasaka K. Tanaka and T. Tanaka Chem. Leu. 1983 1477. 13* Y. Hozumi Y. Imasaka K. Tanaka and T. Tanaka Chem. Lett. 1983 897. I39 T. Yamamura G. Christou and R. H. Holm Inorg. Chem. 1983 22 939. I40 M. H. Chisholm Polyhedron 1982 2 681. R. A. Kok and M. B. Hall Inorg. Chem. 1983 22 728. 196 J.E. Newbery The addition of alcohols to hydrocarbon solutions of 1,~-MO~R~(NM~~)~ gives either 1,2-Mo2R2(OR’) or MO,R(OR’)~ where the rate of the process is markedly dependent upon. steric factors. The replacement of the alkyl group also is much slower than alcoholysis of the amide. The molecule 1,2-Mo,Me2(OBu‘) will take up 2 moles of pyridine and the resultant species142 has been shown to have Mo-Mo of 2.256 A. It is roughly square pyramidal about each metal with one molybdenum occupying the position axial to the other. When the R group is small the alcoholysis reaction proceeds to completion and eventually gives Mo2(OR‘),. With bulky alkyl groups (CH2CMe3 CH2SiMe3 etc.) it becomes possible to isolate species MO~(R)~(OR’), and even the mixed ligand complex MO,(CH~CM~~)~(NM~~)~(OP~~)~.As mentioned previously molybdenum shows a great propensity for sulphur- donor ligands and the preparation of unbridged metal-metal bonded compounds containing monodentate -SR ligands represents a skilful piece of synthetic chemistry.143 Starting from Mo,(NM~~)~ direct addition of (C6H2Me3)SH allows the replacement of only four of the amido groups. A similar process occurs with Mo(OR) as a starting material. However if the complex 1,~-MO,(SBU‘)~(NM~~), is taken addition of the thiol now leads to the production of the desired homoleptic species An X-ray crystallographic analysis confirms this formula- tion and shows themmolecule to be ligated symmetrically with an unbridged Mp-Mo distance of 2.228 A.If (thf)3Li.Sn(SnMe3)3 in hexane is added to a suspension of Mo2C12(NMe2), a heterobimetallic complex is formed with retention of the Mo=Mo bond.’44 Mo2(Sn(SnMe3),},(NMe2) has been studied by X-ray structural methods and shows the usual Mo,X2(NMe2) arrangement of tetrahedral molybdenums with the molecule in the anti conformation. ‘Hn.m.r. evidence supports the retention of this confErmer in benzene solution. Mo-Mo was found to be 2.20 A and Mo-Sn was 2.78 A. Substitution reactions on these M2L6 species usually lead to either cleavage or retention of the M-M bond. For example Mo,(NMe,) will react with 2,6-dimethyl- phenol (HOAr) to give MOz(OAr)6. Use of 4-methylphenol gives14s the complex [H2NMe2]’[Mo2(OAr’),(HNMe2)2]-. An X-ray crystallographic study shows this to possess the overall geometry of a confacial bi-octahedron with terminal amine ligands and three bridging phenoxide ligands (28).The Mo-Mo bond length becomes 2.60 A. The formation of such a different product from a seemingly trivial change in the nature of the phenol raises several interesting points concerning reactivity in this class of compounds. Ar’ Ar’ \I Ar’q ,,\O PAr’ Me,HN-Mo-Mo-OAr’ Ar’d ‘()A \NHMe, I Ar ’ (28) 14* M. H. Chisholm J. C. Huffman and R. J. Tatz J. Am. Chem. Soc. 1983 105 2075. 143 (a) M. H. Chisholm J. F. Corning and J. C. Huffman J. Am. Chem. SOC.,1983 105 5924; (b) M. H. Chisholm J. F. Corning and J. C. Huffman Inorg. Chem. 1983 22 38. I44 M. J. Chetcuti M. H. Chisholm H. T. Chiu and J.C. Huffman J. Am. Chem. Soc. 1983 105 1060. I45 T. W. Coffindaffer I. P. Rothwell and J. C. Huffman Inorg. Chem. 1983 22 3178. Ti,Zr Hf;V Nb Ta;Cr Mo W;Mn Tc Re 197 Gas-phase X-ray photoelectron spectroscopy was used'46 to evaluate core-electron ionization energies in a number of metal-metal tetra-p-carboxylates (M2L4). Ab initio calculations were used to support a model for the metal-metal separations. It was suggested that there is a correlation between the separation and both core and valence metal ionization energies. The large range of Cr-Cr separations in such compounds results from variation in the electrostatic potential at the metal due mainly to the differing charge on the ligands. An example of one of the longer Cr-Cr separations is given in the reported ~tructure,'~' determined by X-ray crystallographic methods of Cr2(02CMe)4(NCS)2.This has the familiar 'paddle-wheel' tetra-po-carboxylates with axial thiocyanates and a very long Cr-Cr separation of 2.467 A. During the course of investigations of the unstable W2C148- some violet crystals shown by analysis to be [W,C19](Ph,PNPPh3)2 were obtained. 149 The cation was characterized by crystallographic means and shown to be a confacial bi- octaeedron (i.e. with three bridging chloro atoms) The metal-metal seqaration was 2.54 A and the metal-chlorine distances were 2.45 A (bridging) and 2.35 A (terminal). The main point of interest here is the considerable lengthening in the W-W bond from that of 2.42 A found in the [W2Cl9I3- ion.This could be explained by suggesting that an increase in the formal metal oxidation number causes a contraction of the 5d orbitals and hence a weaker a-bond. Some of the possible products from reactions between W2(OR) compounds and alkynes are shown in Scheme 8. The cleavage reaction was reported in 1982 but W2(0Bu')6 (Bu'O) WECMe HCCH W2(0Pr')6(py)2 * excess R;C I W2(OPr')6(CL-C4Rk)(C2R:) W,(oR)6(py)(P-N[CMe14N) Scheme 8 the other information is of more recent origin. 150*15' Several noteworthy points arise from a consideration of these sterically-controlled reaction paths. The formulation W,(OR),(py),(p-C,R$) has quite different structures for (R = Pri R = H) and (R = CH,Bu' R' = Me). Whereas the former shows two bridging alkoxy groups the latter has only one and hence different co-ordination about each of the metals.The structure of the (p-C4R3 complex is shown in (29)' and could be viewed as I46 P. M. Atha J. C. Campbell C. D. Gamer I. H. Hillier and A. A. MacDowell J. Chem. Soc. Dalton Truns. 1983 1085. 147 P. D. Ford L .F. Larkworthy D. C. Povey and A. J. Roberts Polyhedron 1983 2 1317. I48 R. R. Schrock L .G. Sturgeoff and P. R. Sharp Inorg. Chem. 1983 22 2801. I49 F. A. Cotton L. R. Falvello G. N. Mott R. R. Schrock and L. G.Sturgeoff Inorg. Chem. 1983,22,2621. 150 M. H. Chisholm K. Folting D. M. Hoffman J. C. Huffman and J. Leonelli 1.Chem. Soc. Chem. Commun. 1983 589. 151 M. H. Chisholm D. M. Hoffman and J. C. Huffman J. Chem. Soc. Chem. Commun. 1983 967.J. E. Newbery C’c II’ Nc RO /C\ /,OR RO-W-W-OR 1 \OR R’C=CR’ R (29) the sum of two segments one having a diene co-ordinated and the other an alkyne. The (N(CMe),N)-containing molecule has the structure shown in (30),with a W-W single-bond distance of 2.617 A. The W-N distances in the N(CMe),N ligand are 1.78 and 2.09 A for the tungsten also bearing the pyridine) and 1.90 8 for the second tungsten. These are not dissimilar from that expected for terminal and bridging imido ligands. If MO,(OR)~(R = Pr’ or But) is reacted with benzoyl peroxide in hydrocarbon solution an intense blue coloration develops.’52 For the propoxy species a solid product was obtained that has a formula Mo~(OP~’),(O,CP~)~. The structure is based about a Mo-Mo double bond with two bridging (OPr’) groups.It is thus formed by edge-sharing octahedra. For R = But the eventual crystalline product was pale yellow-green and formulated MO~(OBU‘)~(O~CP~), where the triple bond has been retained and the 02CPh groups are responsible for bridging. A very interesting transformation occurs when ArN02 is reacted,Is3 under very mild conditions with the M-M triple bonded compound Mo,(CO)~(C~),. The carbonyl groups are expelled and a bridged compound (31) is formed with an Mo-Mo distance of 2.65 A. The decarbonylation process occurs with retention of the metal-metal bond although it drops to single-bond order. (31) (32) (33) Finally for bridged M-M quadruple-bonded complexes the synthesis of a homoleptic phosphide is ann0~nced.l~~ Mo2(p-But2P),(But,P) was produced as a red crystalline solid from the reaction of LiBu‘,P with Mo,(OAc) in diethyl ether.It is quite reactive decomposing rapidly in solution and on exposure to the atmos- phere. The bridging groups in the butterfly configuration (32) are symmetrical and Mo-Mo is 2.209 A. No P-P coupling between the bridged and terminal phosphorus nucleii was observed in the 31P n.m.r. spectrum. Reacting Mo~CI,(PE~~)~ with Me2PCH2CH2PMe2 gave a high yield of the bridged complex Mo,Cl,(diphos), (33) with idealized D symmetry. With an average torsion ‘52 M. H. Chisholm J. C. Huffman and C. C. Kirkpatrick Inorg. Chem. 1983 22 1704. I53 H. Alper J.-F. Petrignani F. W. B. Einstein and A. C. Willis J. Am.Chem. Soc. 1983 105 1701. I54 R. A. Jones J. G. Lasch N. C. Norman B. R. Whittlesey and T. C. Wright J. Am. Chem. SOC.,1983 IM.6184. Ti,Zr Hf;V,Nb,Ta;CryMo,W;Mn,Tc Re angle (x)of 40° the molecule is almost exactly staggered. The metal-metal bond is 2.18 A and is the longest found in compounds of similar stoicheiometry. Indeed it it possible to suggest that an inverse linear correlation exists between the Mo-Mo bond length and cos 2x. This could result from a lessening of the S2 contribution to the quadruple bond as the torsion angle is increased (and therefore as cos 2x decreases). The u27r4contribution is not sensitive to the torsion angle.15s Moving on to clusters containing three or more Group VI metals 95M0 n.m.r. data have been used to examine the nature of the Mo'" aquo Resonances from aqueous solutions of a range of different complexes known to contain the cluster Mo30:+ in the solid state are shown to have chemical shifts of a very similar magnitude.Additional features develop in the spectra after storage of the solutions in air. These are assigned to the formation of some Mo" species probably similar to (MO~O,)~'. A number of reactions of W,(OR) alkynes have already been noted (Scheme 8). If the t-butoxide complex is reacted with EtC2Et for three days at 74 "C a molecule containing six tungsten atoms is formed.'57 This has been formulated [W,(OBu'),(p-O)(p-CEt)O] on the basis of a single-crystal X-ray structural analysis. Each u!it contains a trinuclear tungsten cluster which has two long bonds (W-W ca.2.9 A) that are symmetrically bridged by either -CEt or -OBu' and one short unbridged bond (W-W = 2.42 A). The two trinuclear units are then linked by bis-oxo ligands. There are six electrons available for the metal-metal bonding with the units and bonds of order 2 1/2 and 1/2 might seem suitable. If a slight excess of trimethylphosphite is added to a methanolic suspension of &Mo2C1, the purple colour of the molybdenum salt slowly fades as a yellowish precipitate forms.15* This has the empirical formula MoCl,.P(OMe) and has now been shown to contain a cyclotetramolybdenum feature (34). The four metal atoms form a perfect but not quite rectangular plane (corner angles of 89.5" and 90.5'). (34) The bridged arms are longer than the unbridged (2.878 A and 2.226 A,respectively) and it is suggested that these represent single and triple bonds respectively.Finally in this section on metal-metal bonded compounds two examples are given from amongst the wealth of investigation into heterometallic entities. The titanium reagent (35) is known to add readily across alkyne linkages to form four-membered metallacycles. If it is mixed'59 with W(rCR)(CO),(Cp) such a reaction does not occur; instead a more complicated species (36) can be isolated 15' F. A. Cotton and G. L. Powell Znorg. Chem. 1983 22 1507. IS6 S. F. Gheller T. W. Hambley R. T. C. Brownlee M. J. O'Connor M. R. Snow and A. G. Wedd J. Am. Chem. Soc. 1983 105 1527. F. A. Cotton W. Schwotzer and E. S. Shamshoum Organomerallics 1983 2 1340.F. A. Cotton and G. L. Powell Inorg. Chem. 1983 22 871. I59 R. D. Barr M. Green J. A. K. Howard T. B. Marder I. Moore and F. G. A. Stone J. Chem. SOC. Chem. Commun. 1983 746. 15' 200 J. E. Newbery in which (35) appears to have undergone an insertion reaction in the Ti-C bond. This may be attained via a metallacyclobutene intermediate. A chain-type molecule involving five metal atoms has also been synthesized,’60 (Scheme 9). X-Ray structural analysis was used to ascertain the exact nature of the product at each stage of the stepwise addition of Pt-bis-(cyclo-octa- 1,5-diene) to W(-CR)(CO),Cp. Cp(OCLW /CR II PI II RC’ \W(CO)2Cp Scheme 9 0rganometallics.-The first species to be included here are the carbonyls.During matrix-isolation investigations involving chromium hexacarbonyl a sig- nificant interaction has been observed’61 between a Cr(CO)5 fragment and xenon. The species Cr(CO)sXe is sufficiently stable at -100 “C to allow identification by the characteristic pattern of carbonyl bands in the FT-i.r. spectrum. The anionic species [M(CO),X,]- (M = Mo or W and X = Br or I) can be prepared’62 by refluxing M(CO)5py with the appropriate halogen. If bipyridyl is now added the complex M(C0)3(bipy)X2 is produced. I 60 M. R. Awang G. A. Carriedo J. A. K. Howard K. A Mead I. Moore C. M.Nunn and F. G. A. Stone J. Chem. SOC.,Chem. Commun. 1983 964. 161 M. B. Simpson M. Poliakoff J. J. Turner W. B. Maier 11 and J. G. McLaughlin J. Chem. SOC.,Chem.Commun. 1983 1355. I62 J. R. Moss and B. J. Smith S. Afr. J. Chem. 1983 36 33. Ti Zr Hf;V Nb Tu;Cr Mo W;Mn Tc Re 20 1 Cr(CO)S(S02) has been studied by X-ray crystallographic methods and to have 7 I-co-ordinated sulphur dioxide. The carbonyls are virtually all equally distant from the metal and this is taken as proof of the high w-acceptor power of SOz. At 219 pm the Cr-S separation is one of the shortest reported. The compounds M(CO)5(SCH2SCH,SCH2SdH2)(M = Cr or W) have been by variable temperature n.m.r. and evidence has been collected for two intramolecular processes. There was no free ligand exchqnge and it seems likely that the processes are a pyramidal inversion about the co-ordinated sulphur atom (37) with an activation energy of 50 kJ mol-I and a 1,3 shift with E of 80 kJ mol-I.Both had AS* of near zero. (37) A series of W(CO),L sulphide complexes where L = R3ZSPh with R = Me or Ph and Z = C Si;Ge or Sn has been prepared.'65 These were studied by observing the y(C0) frequencies which change in response to alterations of the electron density on the sulphur. Several reports on n.rn.r. investigations of Group VI carbonyl complexes have appeared recently. 31P resonances in an extensive series of complexes of formulation W(CO),(PR,)(L) show'66 that the cis has a larger shift than the corresponding trans isomer. In the trans complexes the W-P coupling constant depends upon the nature of L; J decreases in the order SbPh3 <AsPh <PPh -P(OPh) <CO. I3C spectra for a number of Cr(CO)5L complexes a correlation between the oxidation potential and the I3C chemical shift.95M0 spectra have also been obtained16' and perhaps the most interesting is that while the 95M0 shifts seem to show very poor correlation with chemical shifts of other nucleii they do seem to correlate with A,, of the charge-transfer bands. The homoleptic complex Cr&(R = CPh=CMe,) is a green crystalline material that is relatively stable to the atmosphere. It can be formed17' by treating Li(CPh=CMe,) with CrC13.3(thf) and has been shown t? have an approximate tetrahedral structure with Cr-C distances of 2.98 f 0.02 A. Terminal methylidyne groups on tungsten have been shown to be not very willing to react with carbon monoxide unless aluminium reagents are also present.A complex formulated W(CH)(CO),(PMe3)3(C1)(A1X3) can be ~btained'~'from reacting W(CH)(PMe,),Cl with CO and AlMe (or A12C16). This has now been shown to 163 Ch. Burschka F.-E. Baumann and W. A. Schenk Z. Anorg. Allg. Chem. 1983 502 191. 164 E. W. Abel G. D. King K. G. Orrell and V. Sik Polyhedron 1983 2 1363. 165 C. R. Lucas Can. 1.Chem. 1983 61 1096. I66 W. A. Schenk and W. Buchner Inorg. Chim. Actq 1983 70 189. I67 A M. Bond S. W. Carr R. Colton and D. P. Kelly Inorg. Chem. 1983 22 989. I68 A. F. Masters G. E. Bossard T. A. George R. T. C. Brownlee M. J. O'Connor and A. G. Wedd Inorg. Chem. 1983 22 908. 169 G. M. Gray and C. S. Kraihanzel Inorg. Chem. 1983 22 2959. I70 C J. Cardin D. J. Cardin J. M. Kelly R.J. Norton A. Roy B. J. Hathaway and T. J. King J. Chem. Soc. Dalton Trans. 1983 67 1. 171 M. R. Churchill and H. J. Wasserman Inorg. Chem. 1983 22 41. 202 J. E. Newbery correspond to the structure (38) W( q2-HCrCOA1C13)(CO)(PMe3)3Cl.The q2-ligand has W-C distances (2.03 and 2.01 A) close to those of carbon-tungsten double bonds found in alkylidene complexes. It is also interesting to observe that the plane of the ligand is parallel to the bonding axis of the carbonyl group. 713 A1 I 0,C-CH OC:wyPMe3 \/ Me,P 1 PMe C1 (38) (C6Et6)Cr(C0)2CS has a ‘piano-stool’ structure in the solid state with the ethyl groups projecting alternately ‘up’ and ‘down’ around the ring.’72 The 13C n.m.r. spectrum in CD2C1 solution at 163 K is consistent with this conformation.As the temperature is raised the ring begins to rotate about the Cr-centroid axis with subsequent spectral alterations. The paramagnetic piano-stool molecule CpMo(Cl),(diene) will ~ndergo”~ the expected metathetical halogen exchange with TlSAr (Scheme lo) but an excess of reagent will expel the diene and produce a diamagnetic molecule CpMo(SAr),Tl. TlSAr (excess) (excess) nSAr 1 1 CP CP I I I SAr (B) Scheme 10 Two possible structures A and B are consistent with spectroscopic data. Thus for Ar =C6F5,19Fn.m.r. spectra show four inequivalent aromatic groups and evidence for exchange between bridging and terminal -SAr groups was obtained. One of the carbonyl groups in (C~)MO(CO),{[CH,]~B~} becomes incorporated into a cyclic three-electron ligand if the complex is treated with LiEt3BH in thf.I7 I72 M.J. McGlinchey J. L. Fletcher B. G. Sayer P. Bougeard R. Faggiani C. J. L. Lock A. D. Bain C. Rodger E. P. Kiindig D. Astruc J.-R. Harnon P. Le Maux S. Top and G. Jaouen J. Chem. Soc. Chem. Commun. 1983 634. ‘73 J. L. Davidson. K. Davidson and W. E. Lindsell 1.Chem. Soc. Chern. Cornmun. 1983 452. I74 H. Adarns N. A. Bailey P. Cahill D. Rogers and M. J. Winter J. Chem. Soc. Chern. Cornmun.,1983 831. Ti,Zr Hf; V Nb Ta; Cr Mo W;Mn Tc Re 203 The sotructure adopted is sho!n in (39) and both (Mo-C) (ring) and (Mo-0) are 2.16 A with C-0 (ring) 1.41 A. The Mo-0 interaction can be readily interrupted and thus the compound will take up 1 mole of PPh3 in high yield with the cyclic ligand remaining attached to the metal via the carbon alone.CP I H,C-CH2 (39) 5 Manganese Technetium and Rhenium A review has been written17' on the role of manganese in photosynthetic oxygen evolution. Mn207 has been known as a highly explosive substance for over 100 years and probably as a result of this property there is little known about its structure. Both i.r. and U.V. spectra have now been recorded'76 for matrix-isolated species at low temperatures. The spectra are consistent with a bridged 03Mn-0- Mn03 structure and v(Mn=O) was found at 995cm-' (asymm) and 890cm-' (symm) with v(Mn-0) at 775 cm-'. The bridge angle is probably around 155". EXAFS measurements were to suggest that aqueous solutions of MnBr2 have MnBr2(H20) present as the major species.This was achieved by a comparative method involving an examination of the aquo solution and of the crystalline compounds MnBr,.2H20 and MnBr2.4H20. Co-ordination Compounds.-These will be examined metal-by-metal in order of ligand complexity. There has been some controversy over the manganese(I1) complexes Mn(t-phos- phine)X2 concerning whether these species have any existence and if so whether they can bind oxygen reversibly. By releasing phosphine vapour on to a film of MnBr, changes in the i.r. spectrum could be observed.'78 These have been interpreted as strong evidence for the existence of the complex MnBr2.PMe,. No evidence could be found for reversible oxygenation but dioxygen is taken up as a superoxide species eventually giving rise to a phosphine oxide complex.There are no such status doubts concerning malate complexes of Mn". An X-ray crystallographic analysis of manganese( 11) (*)-1-malate confirms' 79 the expected octahedral environment about the metal with the ligand chain in the trans conforma-tion. There is hydrogen bonding present also and each malate ion has an interaction with three manganese centres. Not surprisingly I-cysteine proves to be a better ligand to manganese(") than the cysteine molecule with a methyl group substituted at the N S or ester positions.'80 Oxygen uptake occurs in solutions of the cysteine complex with the ligand eventually L.-E. Andriasson 0. Hansson and T. VanngHrd Chem. Scr. 1983 21 71.17' W. Levason J. S. Ogden and J. W. Tufi J. Chem. SOC.,Dalton Trans. 1983 2699. I77 B. Beagley B. Gahan G. N. Greaves and C. A. McAuliffe J. Chem. Soc. Chem. Commun. 1983 1265. 178 H. D. Burkett V. F. Newberry W. E. Hill and S. D. Worley J. Am. Chem SOC.,1983 105 4097. 179 A. T. H. Lenstra and J. Dillen Bull. SOC.Chirn. Belg. 1983 92 257. 180 R. K. Boggess J. R. Absher S. Morelen L. T. Taylor and J. W. Hughes Inorg. Chem. 1983 22 1273. 204 J. E. Newbery forming a disulphide. The manganese ion acts in a catalytic fashion probably through an Mn"'/02 species. Mn(NCS)2(pyrazole) has been shown by single-crystal X-ray diffraction to take the trans configuration."' The chemistry of technetium now yields almost as many papers for review as that of manganese.The production of stable Tc' complexes such as [Tc(CNR),]+ by Na2S204 reduction of the pertechnetate in the presence of the ligand has been reported.lS2 The method worked well for R = Me But cyclohexyl and Ph and only failed for R = H. The complexes are air and water stable and can be oxidized at ca. 0.85 V (versus SCE) for the alkyl and 1.18 V for the phenyl species. Synthesis of a number of Tc-substituted-thiourea complexes is reported. 183,184 The low-spin d5 Tc" complex TcCl,(NO)( PMe2Ph) can be readil~''~ prepared from TcCl,(PMe,Ph). E.p.r. data are interpreted as giving evidence for the mer-arrangement of chlorines with trans phosphine groups. Much of the interest in technetium is a result of its employment as an image- forming substance in nuclear medicine.Cationic complexes are thus of some poten- tial use in scanning body tissue such as the heart with a propensity for the accumulation of positively charged entities. A number of such complexes of general formula tran~-[Tc(diphos)~X~]+ = C1 Br or NCS) have been prepared.lS6 The (X corresponding Tc"' neutral compounds were also prepared. Reduction methods from TcCli- TcOCl ions were used in each case. Crystal structures on some octahedral rhenium compounds have been reported. 187-'89 ReI,O(OR)(PPh,), where R = Me or Et takes the all-trans form."' Perhaps the most interesting part of the structure is the I-Re-I bond angle which is 166.9' in the ethoxy case and 169.8' in the methoxy example. From a mixture of ReCl, (NSCI), and P0Cl3 both (Cl,PO)ReCI,NSCl and (C13PO)ReC13(NSC1)2can be isolated."' If the latter species is now treated with AsPh,Cl in dichloromethane a cationic complex [ReCl,(NSCl),]- is precipitated.This has cis-NSC1 groups with Re-N-S nearly linear (175.3' and 175.9') and the angles N-S-Cl of ca. 108". If ReCl,(NO) is reacted with triphenylphosphane (NPPh,) a complex involving triphenylphosphine oxide is produced.lS9 This has been characterized as ReCl,(NO)(NPPh,)(OPPh,) by P n.m.r. spectroscopy and X-ray crystallography. It shows mer-chlorines with the OPPh3 group trans to the bent nitrosyl (Re-N-0 = 174.1'). One interesting feature of Group VII chemistry is the wide amount of attention paid to complexes involving macrocyclic ligands.As well as being used for organ- imaging technetium compounds are possible chemotherapeutic agents. In this 181 P. Lumme I. Mutikainen and E. Lindell Inorg. Chim. Acra 1983 71 217. 182 M. J. Abrams A. Davison A. G. Jones C. E. Costello and H. Pang Inorg. Chem. 1983 22 2798. '83 U. Abram and S.Abram Z. Chem. 1983 23 228. I84 M. J. Abrams D. Brenner A. Davison and A. G. Jones Inorg. Chim. Acta 1983 77 L127. 185 R. Kirmse B. Lorenz and K. Schmidt Polyhedron 1983 2 935. '*' K. Libson B. L. Barnett and E. Deutsch Inorg. Chem. 1983 22 1695. 187 G. Ciani G. D'Alfonso P. Romiti A. Sironi and M. Freni Inorg. Chim. Acta 1983 72 29. I88 U. Muller W. Kafitz and K. Dehnicke Z Anorg. Allg. Chem.. 1983 501 69. N. Mronga F. WeIler and K. Dehnicke.2.Anorg. Allg. Chem. 1983 502 35. I89 Ti Zr Hf;V Nb Ta;Cr Mo W;Mn,Tc Re context the synthesis and tissue distribution of 99Tc tetrasulphophthalocyaninesis of some interest."' While there was little interaction with the stomach or thyroid useful amounts were found to be retained by the cortex of the kidney and also the liver. Possible interaction with tumours was also observed. R-N \ /"-" N N (40) A template synthesis involving the formation of the ligand shown in (40) is reported.'" The product was formed from the condensation of 2,9-di(N-2'-hydroxyethylhydrazin0)- 1,lO-phenanthroline with 2,6-diacetylpyridine in the pres- ence of maganese chloride. Mn(L)Cl has the metal co-ordinated by five of the ligand nitrogen atoms (0.51 A above their plane) and has the chlorine in the axial site.The strength of the manganese-nitrogen bond in nitridomanganese porphyrins is shown192 by the fact that it is possible to undertake reductive methylation on the octaethyl porphyrin complex and yet retain the MnEN bond. The methylated compound shows Mn-N of I .5 12 A. Mn'"(tpp)(L), where L = N; or NCO- and tpp = tetraphenylporphinato can be made"' from Mn(tpp)(OMe) by reaction with either Me,Si.N or HNCO. The complexes are rather unstable but it proved possible to show that the isocyanato species is roughly octahedral about the manganese. There is considerable 'ruffling' of the porphyrin core which may be a result of crystal-packing constraints; Mn-NCO is 1.93 A. Oxygen-transfer is an obvious area of interest for porphyrin species.Treatment of a dichloromethane solution of Mn(tmp)Cl where (tmp) is tetramesitylporphinato by aqueous sodium hypochlorite in the presence of a phase-transfer agent caused the initially green organic layer to turn brown.194 [Mn(tmp)O]Cl is rapidly reduced back to the Mn"' starting complex. It will however react with both styrene or triphenylphosphine to give the appropriate oxide. Mn"'(tmp)CI can also be reacted with potassium superoxide (in acetonitrile- crown ether) to give195 Mn"(tmp)O,. Both species have been shown capable of fitting into a complete catalytic scheme involving acylation and also oxygen-transfer to olefins (Scheme 11). 1.r. spectra have been obtained for Mn(oep) and Mn(oep)O, where oep = octaethylporphinato by the matrix-isolation method.19' The v( 1602) peak occurs at I YO J.Rousseau D. Autenrieth and J. E. van Lier Inf. J. Appl. Radiaf. Isor. 1983 34 571. 191 C. W. G. Ansell J. Lewis P. R. Raithby and T. D. O'Donoghue J. Chem. Soc. Dalton Trans. 1983 177 192 J. W. Buchler C. Dreher K.-L. Lay Y. J. A. Lee and W. R. Scheidt Inorg. Chem. 1983 22 888. I93 M. J. Camenzind F. J. Hollander and C. L. Hill Inorg. Chem. 1983 22 3776. 194 0. Bortolini and 8. Meunier J. Chem. Soc. Chem. Commun. 1983 1364. I95 J. T. Groves Y. Watanabe and T. J. McMurry J. Am. Chem. Soc. 1983 105 4489. 196 T. Watanabe T. Ama and K. Nakamoto Inorg. Chem. 1983 22 2470. J. E. Newbeiy Scheme 11 991 cm-' which is very similar to that obtained for Mn(tpp)O where the dioxygen is known to exhibit side-on co-ordination.Manganese(rv) is not a notably stable oxidation state and yet from an aqueous alkaline melange of the cyclic amine 1,4,7-triazacyclononane,manganese chloride oxygen and sodium bromide crystals of a stabie MnIV bridged cluster (41),were obtained. The complex is formulated [(tria~)~Mn~O~]~+ and is based on an adaman-tane-like cage with near octahedral co-ordination about each metal from three bridging oxygen ligands and one triazacyclononane ligand. It is stable in both neutral \I/ 0-Mn" /\ 19' and alkaline solutions. Not surprisingly the most interesting metal-metal bond items come from the chemistry of rhenium. Reaction between Re2CI,(PBu;) and Ph2P-py in methanol gavel9* red-purple crystals of composition Re2Cl3(Ph2Ppy),.However the structure is more complicated than this since o-metallation of one of the phenyl rings has occurred. This is shown in (42)as a view along the Re-Re axis with two axit1 chlorines omitted from the diagram for clarity. The Re-Re triple bond is 2.336A and the axial chlorines deviate from Re-Re-Cl linearity by 13-18". I97 K. Wieghardt U. Bossek and W. Gebert Angew. Chem. Int. Ed. Engl. 1983 22 328. I98 T. J. Barder S. M. Tetrick R. A. Walton F. A. Cotton and G. L. Powell J. Am. Chem. Soc. 1983 105 4090. Ti,Zr Hf;V Nb Ta;Cr Mo W;Mn Tc Re 207 A series of di-rhenium complexes Re2C1,(PR,) (n + rn = 8)' with bond orders of 3 3.5 and 4.0 has been prepared.'99 No direct response could be found for the Re-Re bond length from these changes in bond order.0rganometallics.-Ultrasonic irradiation of liquids produces acoustic cavitation and the rapid growth and decay of these short-lived vacuoles generates local 'hot-spots' of both temperature and pressure.2w With M2(CO),o (M = Mn or Re) ultrasound ('sonochemistry') promotes ligand substitution by phosphines or phos- phites.201 The reaction rate was found to be roughly first-order in metal carbonyl but independent of the concentration or the nature of the ligand. The decacarbonyls Mn2(CO),o and Re2(CO)lo are known not to 'scramble' (e.g. by refluxing in decalin) and even isotopic scrambling for the rhenium takes place only in the absence of carbon monoxide. Thus reversible homolytic fission is not exactly fashionable in this area of chemistry.For Mn2(C0)8L2 {L = PPh or P(cyc1o- hexyl),} the formation of ClMn(CO),L by reaction with C1,CH.CHC12 is shown202 to follow a mechanism that relies upon initial homolysis of the Mn-Mn bond. Apart from the obvious mechanistic checks verification for this path was obtained by observing the formation of scrambled Mn( CO),( PPh,).Mn( CO),.P(cyc) during a reaction involving both complexes simultaneously. U.V.photolysis of HMn(CO)S in an isolated matrix is known to promote the loss of one carbonyl ligand. A combination of 13C0 enrichment and i.r. spectroscopy has been usedZo3 to show that the product HMn(CO), has the C (square-pyramidal with an apical carbonyl) structure rather than the earlier C, suggestion.The C, variant (where the hydride takes the apical position) can be produced by photolysis at lower energies (A = 403 nm for Ar matrix). The compound Mn2(CO),(Ph2P-CH2-PPh2)2(p-H)(p-Br) can be decarbony-lated204 by treatment with lithium aluminium hydride to give a bridged dihydride (Scheme 12). This species has been assigned a Mn=Mn on the basis of spectroscopic and crystallographic evidence as well as by the requirements of the 18e rule. It has been shown to undergo a number of interesting substitution reactions. A thiazylfluoro complex of rhenium can be producedZo5 by reacting NSF with [Re(CO),(SO,>]+ to give [Re(CO),NSF]+. This cation is quite stable in a solution of liquid SO2 and can be usedzo6 to form thiazylamides by the addition of Me,SiNMe,.[(OC),ReNSF]+ + Me,Si.NMe + [(OC),Re(NSNMe,)]+ + Me,SiF The rhenium has been shown to be octahedral with a Re-N single bond of 216 pm and the angle Re-N-S of 130". Mn" aryl species tend to be somewhat unstable and the homoleptic Mn3(mesityl) proved too sensitive to allow microanalytical determinati~n.~'~ It was produced by I99 F. A. Cotton K. R. Dunbar L. R. Falvello M. Tomas and R. A. Walton J. Am. Chem. Soc. 1983 105 4950. 200 K. S. Suslick J. W. Goodale P. F. Schubert and H. H. Wang J. Am Chem. SOC.,1983,105 5781. 20 I K. S. Suslick and P. F. Schubert J. Am. Chem. SOC.,1983 105 6042. 202 A. Po2 and C. Sekhar J. Chem SOC.,Chem. Commun. 1983 566. 203 S. P. Church M. Poliakoff J. A. Tirnney and J. J. Turner Znorg.Chem. 1983 22 3259. 204 H. C. Aspinall and A. J. Deeming J. Chem. SOC.,Chem. Commun. 1983 838. '05 R. Mews and C.4. Liu Angew. Chem. Int. Ed. Engl. 1983 22 162. G. Hartmann R. Mews and G. M. Sheldrick Angew. Chem. Znf. Ed. Engl 1983 22 723. 207 S. Gambarotta C. Floriani A. Chiesi-Villa and C. Guastini J. Chem. SOC.,Chem. Commun. 1983 1128. J. E. Newbery li Reagents i LiAIH,; ii CO; iii P(OMe),; iv MeNC Scheme 12 reacting MnCl with the appropriate Grignard reagent and has been formulated on the basis of X-ray crystallographic evidence. It has a linear-chain metallic core (angle Mn-Mn-Mn of 178.8') with each pair bridged by two mesityl groups. The remaining two groups are axial. The central metal is in a roughly tetrahedral site whilst the terminal metals are trigonal.Mn" is also tetrahedra1208 in Mn(CH2CMe,Ph)(PMe3), which was formed by the cleavage reaction Mn,R,(PMe,) + 2PMe * 2MnR,(PMe,) A tetrahedral benzyl species of presumably similar structure was formed when MnCl, diphosphine and Mg(CH,Ph) were reacted. (The diphosphine was used to counteract the tendency for PMe to be lost from the complex.) If the Grignard o-C6H4(CH2MgC1) was substituted for Mg(CH,Ph), however a six-co-ordinate product Mn(~-(CH,)~C~H,)(diphos)~ was formed. This is presumably a result of the ortho-ligand requiring less space at the metal and thus allowing a secondediphosphine to co-ordinate. Despite this the Mn-C distances are shorter (ca. 2.1 A) than those C. G. Howard G. S. Girolami G. Wilkinson M.Thornton-Pett and M. B. Hursthouse J. Chem. SOC. Dalton Trans. 1983 263 1. Ti,Zr Hf;V Nb Ta; Cr Mo W;Mn Tc Re of the tetrahedral complex (ca. 2.15 A) while the Mn-P distances are as much as 0.4 A shorter. The addition of methyl-lithium to a diethyl ether mixture of Me2PC2H4PMe2 and Mn"'( a~etylacetonate)~ gave a clear yellow solution.209 After extraction with petroleum spirit crystals can be obtained of both MnMe,(diphos) and MnMe,( diphos) ; it thus suggested that a disproportionation reaction (2Mn"' + Mn" + MnIV) has occurred. The magnetic moment (3.87 pB)of the former complex product is consistent with that expected for d3 MnIV. X-Ray diffraction data show an octahedral structure for the MnIV complex with the Mn-C bonds trans to !he phosphorus slightly shorter (2.06 and 2.09 A) than those alkyls mutually cis (2.12 A)..I Mn-Mn-Mn (43) The complex Mn (3-MeC5H,) was isolated2" from the reaction between MnCl and the 3-methylpentadienyl anion. Both X-ray structural analysis and variable- temperature magnetic susceptibility support a formulation as a high-spin complex. There is a near (177.5") linear trimetallic arrangement (43). Each ligand has one end co-ordinated to the central metal and this causes a near staggered configuration to be adopted about the terminal metals (with an inter-Iigand rotation angle of 35.4"). ZOY C. G. Howard G. S. Girolami G. Wilkinson M. Thornton-Pett and M. B. Hursthouse J. Chem. Soc. Chern. Commun. 1983 1 163. M. C. Bohm R. D. Ernst R.Gleiter and D. R. Wilson Znorg. Chem. 1983 22 3815.