11 Cr Mo,and W By H. SLOAN Consulting Chemist 40 Wendan Road Newbury Berkshire RE14 7AF UK 1 introduction This report covers the chemistry of Clr Mo and W for the two years 1991 and 1992. It is organized in part by structural type and in part by the major ligand donor atom. Reviews have appeared on 19-electron organometallic adducts of molybdenum,' molybdenum and tungsten oxide zeolites, cubane and incomplete cubane-type Mo and W oxo/sulfido cluster^,^ cyclopentadienyl molybdenum and tungsten dihalide~,~ coordination chemistry and catalysis with oxygen-phosphorus ligand complexes of chromium,' two- or three-fold orientational disorder6 in [M2X8]"- [M2X,L4] and [M,X,(P-P),] and cubane Mo W clusters with [S,P(OC,H,),] -ligand~.~ Metalates are described in reviews of polyoxomolybdates and tungstates,8 the coordination chemistry of polyox~molybdates,~ nitrosyl-substituted anions," and thiometalate complexes'' of the Cu-Mo/W-S system.Aspects of the chemistry of this group are also included in wider reviews of transition metal hydrides' (tungsten) protonation of coordinated dinitrogen' (molybdenum and tungsten) nitrido complexes of transition metalsI4 (molybdenum and tungsten) transition metal fluoro compounds containing CO PR, AsR, SbR ligands," di- tri- and polyphosphine complexes of transition metals," ab initio calculations of transition metal organometallics' '(chromium),ab initio molecular orbital studies of catalytic reactions of transition metal complexes,'8 transition metal and enzyme- ' D.R. Tyler Ace. Chem. Res. 1991 24 325. G.A. Ozin S. Ozkar and R. A. Prokopowicz Ace. Chrm. Res. 1992 25. 553. T. Shibahara Adu. Inorg. Chem. 1991 37 143. M. L.H. Green and P. Mountford Chem. Soc. Rev. 1992. 21 29. ' A. Bader and E. Lindner Coord. Chem. Rev. :991 108 27 (pages 40-44). ' F.A. Cotton and J. L. Eglin Inorg. Chim. Acta 1992 198-200 13. ' S. Lu J. Huang H. Zhuang J. Li D. Wu Z. Huang C. Lu J. Huang and J. Lu Polyhedron 1991,10,2203. ' M. T. Pope and A. Muller Angew. Chem. Int. Ed. Engl. 1991 30. 34. ' Q. Chen and J. Zubieta Coord. Chem. Rev. 1992 114 107. lo Y. Jeannin G. Herve and A. Proust Inorg. Chim. Acta 1991 198-200 319. " Y. Jeannin F. Secheresse S. Bernes and F. Robert Inorg. Chim. Acta 1991 198-200 493. 'Transition Metal Hydrides' ed.A. Dedieu VCH 1992. l3 G.J. Leigh. Ace. Chem. Res. 1992. 25 177. K. Dehnicke and J. Strahle Angew. Chem. Int. Ed. Engl. 1992. 31 955. N. M. Doherty and N. W. Hoffman Chem. Rep. 1991 91 553. Ib A.-M. Caminade J.-P. Majoral and R. Mathieu Chem. Rep. 1991 91 575. A. Veillard Chem. Rev. 1991 91 743. N. Koga and K. Morokurna Chem. Rev. 1991. 91 823. 127 128 H. Sloan catalysed reactions involving NH and amines,” solid state NMR of coordination compounds,20 hydrogen isotope exchange rates for polyamines bound to inert complexes2’ (chromium) optically-detected magnetic resonance spectroscopy of coordination compounds22 (chromium and molybdenum) reactions of transition metal dihydrogen complexes23 and complexes of silylenes silenes etc.24 2 Bond Stretch Isomers The existence of bond-stretch isomers has been the subject of a number of reviews2’ Reinvestigation has provided evidence in some cases that the apparent bond length isomerism is associated26 with co-crystallization of two compounds often where the difference in composition relates only to a metal-chloro or metal-oxo bond. Two forms of [MoOCI,(PMe,Ph),] and the dibromo analogue are reported2’ where differences of angles as well as some bond lengths occur though other investigators have disagreed.28 Ab initio calculations for [WOCl,(Me,tacn)] indicate29 that there is only one ground state and an orbital crossing mechanism cannot explain the occurrence of two isomers. For cis,mer-[Mo0C1,(PR3),] the second order Jahn-Teller effect is too weak to cause the bond-stretch phenomenon.In both cases calculations support the shorter bond as the stable form. Similar problems in distinguishing between Mo-0 and Mo-C1 bonds are de- scribed3’ in a structural determination of mer,~is-[MoOC1~(OPPh,)~] (1) where there is disorder between oxygen and chlorine atoms related by a crystallographic two-fold axis. This form is isomorphous with the corresponding W compound. A previous structural determination of a different form of (1) showed31 significantly different Mo-Cl and Mo-0 bond lengths for an ordered structure. 3 Metalates Topological aspects of polyoxometalates have been discussed.32 Polytungstate anions are often studied with regard to reductive and catalytic potential.The most frequently studied Keggin-type anions with varied central heteroatom and with substitution of a few tungsten atoms by other transition metals on the surface of the anion show variations in anionic charge and charge distribution that affects this potential. Though the surface substitution often leads to disorder in the l9 D. M. Roundhill Chem. Rec. 1992 92 1. ’” J. A. Davies and S. Dutremez Coord. Chem. Rw. 1992 114 201. ” D.A. House Coord. Chem. Reu. 1992 114 249. 22 A. L. Kanyshny A. P. Suisalu and L.A. Aslanov Coord. Chem. Rev. 1992 117 1. 23 P. G. Jessop and R. H. Morris. Coord. Chem. Rev.. 1992 121 155. 24 P.D. Lickiss Chem. SOL..R~L,., 1992 21 271. 25 G. Parkin Acc. Chem. Res. 1992,25,455;J. M. Mayer Angew. Chem. Int. Ed.Engl. 1992,31,286; V.C. Gibson and M. McPartlin. J. Chem. Soc. Dalton Trans.. 1992 947. 26 K. Yoon G. Parkin. D. L. Hughes and G.J. Leigh. J. Chem. Soc. Dalton Trans. 1992 769. 27 A. P. Bashall S. W. A. Bligh. A. J. Edwards V. C. Gibson M. McPartlin and 0.B. Robinson Angew. Chem.. Int. Ed. Enyl. 1992 31. 1607. K. Yoon G. Parkin and A. L. Rheingold J. Am. Chem. Soc. 1991 113 1437; K. Yoon. G. Parkin and A.L. Rheingold J. Am. Chem. Soc. 1992 114 2210. 29 J. Song and M. B. Hall Inorg. Chem. 1991 30 4433. 3” B. E. Owens and R. Poli. Acta Crystullogr. Sect. C 1992 48 2137. 3’ C. D. Garner N. C. Howlader F. E. Mabbs A. T. McPhail and K. D. Onan J. Chem.Soc. Dalton Trans. 1978. 1848. 32 R. B. King Inorg. Chem.. 1991 30 4437. Cr Mo and W 129 crystal state making identification of the substituted sites difficult the anion [PTi,W 10040]7 -showed3 a preferred orientation and location of the titanium atoms as a c isomer.The isomorphous ammonium salts of [MW,,O,,F,NaH,]"-(M = Co n = 9; M = Fe n = 8) have 34 Dawson-type structures. Tandem MS was shown to be a useful technique for the characterization of large inorganic complexes. Reaction of Na,MoO with A-Na,[PW,O,,] gave3 [PMo,W,O,,]~- which is an A-type trisubstituted p-isomer with the three MOO moieties linked together in a triangle on one side of the anion. Addition of sodium metavanadate to the divacant anion y-[HSiW 10036]7 -gave,3h quantitatively the 1,2-divanado-compound Cs,H,[y-SiV W ,OO,O]. This complex is stable in non-aqueous solutions but isomerizes in water to the ,&structured (8,12) (3,12) or (3,8) divanado-isomers.The anion of K,Na4H,[TbWlo0,,] is made37 from two W,Oy groups chelating the central terbium atom. The W,Oy groups are derived from the [W,0,,]2 -ion by removal of a W04+ unit. Two of the potassium ions are coordinated to the anion in the crystal playing a stabilizing r61e that apparently cannot be provided by sodium ions; the all-sodium salt could not be prepared. The ;I-octamolybdate [M~,N(CH,),NM~,][MO,~~~] from a slightly ~rystallized,~ acidic aqueous solution of sodium molybdate and [Me,N(CH,),NMe,]CI,. The anions contain six edge-sharing MOO octahedra and two MOO trigonal bipyramids contrasting with the a-form (six octahedra and two MOO tetrahedra) and p-form (eight octahedra).Reaction of [NBU,],[MO~~PO,~] with PPh in MeCN gave39 the two- and four-electron reduced compounds containing one or two molybdenum(v) pairs where a bridging oxygen atom has been eliminated. The anion retains the Keggin-type structure. An exchange reaction involving transfer of a bridging oxygen atom between [Mo~~Mo~PO,,]~-occurs in solution within the NMR and [Mo~'Mo~PO,,]~- timescale. The aluminomolybdate K3H6[AlMo,0,,]~7H20 has4' a typical Anderson-type anion with MOO octahedra sharing edges with an almost regular central A10 octahedron. [NBuf;],[TeMo,O,,(OH,)] was prepared4 by the reaction of Te(OH) and [NBuf;],[Mo,O,,]. The X-ray crystal structure revealed the presence of discrete anions containing a distorted square-pyramidal MoV' atom.This contrasts with the only other structurally characterized five-coordinate MoV1 compound [MoO,{C,H,N(CH,P~,S)~)] which is trigonal bipyramidal. The isostructural arsenometalates Na,[As,M,O,,]~lOH,O (M = Mo W) have4 an M30, block stabilized by a linear triarsenate moiety. The arsenomolybdate anion reacts with Co2 + 33 T. Ozeki and T. Yamase Acta Crystallogr. Sect. C 1991 47 693. 34 S. H. Wasfi C. E. Costello A. L. Rheingold and B. S. Haggerty. Inory. Chem.. 1991. 30 1788. 35 I. Kawafune and G. Matsubayashi Chem. Lrrt.. 1992 1869. 36 J. Canny R. Thouvenot A. Teze G. Herbe. M. Leparulo-Loftus and M. T. Pope Inorg. Chmi.. 1991.30 976. " T. Ozeki. M. Takahashi and T. Yamase. Acfu Crystallogr. Sect. C. 1992 48 1370. 38 M.L. Niven J. J. Cruywagen and J. B. B. Heyns J. Chem. Soc. Dulron Truns. 1991 2007. 39 I. Kawafune and G. Matsubayashi Inorg. Chim. Actu. 1991 188. 33. 40 H.Y. Lee K. M. Park U. Lee and H. Ichida. Acfa Crystalloqr. Sect. C 1991,47 1959. 41 H. Ichida and A. Yagasaki. J. Chem. Soc.. Chern. Commun.. 1991. 27. 42 J. Martin-Frere Y. Jeanin F. Robert and J. Vaissermann. Inory. Chem. 1991. 30. 3635. 130 If. Sloan to give [C~(H,O),]I(,[A~,M~,~O~~~] which has an Anderson-type structure with the top and bottom of the anion having a tripod of corner-sharing AsO moieties on an equatorial band of MOO octahedral around a central cobalt atom. Bridging molybdate groups occur43 in the neutral complex [LF~(MOO,)~F~L]CH,C~~-H~O l2 -consisting of (L = Me,tacn) (2).The anion [Te,Mo 2060]has a novel ~tructure,4~ a ring of distorted TeO octahedra with pairs of MOO octahedra sharing one oxygen (3).Adjacent pairs of MOO octahedra share oxygen atoms with each other and with TeO only so there is no continuous -0-Mo-0-Mo-0-Mo-pathway. (Reproduced by permission from J. Chem. SOC. Chem. Commun. 1992 248) Another route to modification of catalytic properties with possible intermediates from catalytic reactions in mind is the attachment of ligands to the surface transition metal atoms in place of terminal 0x0 groups. The hexamolybdate anion [Mo,O J2 -reacted45 with Ph,P=Ntol to give an imido ligand (Mo=Ntol group). This is easily 43 K.Lettko S. Liu. and J. Zubieta. Actu Crysrulloqr. Sect. C. 1991 47. 1723.44 C. Rob1 and M. Frost. J. Chem. Soc,.. Chem. Commun.. 1992. 248. 45 Y. Du. A. L. Rheingold and E.A. Maatta. J. Am. Chem. So(,..1992 113 345. Cr Mo and W 131 hydrolysed to p-toluidine and the original molybdate anion. The Mo-0 bonds adjacent to the imido ligand are significantly shortened. 4 Cubane-type Structures A cuboidal arrangement M,X, of four metal and four Iigand donor atoms with each of these groups of four occupying alternating corners of the cube has become a well-recognized structural type. The X atoms are often oxygen or sulfur either as the single atom or as part of a ligand or halogen and are not always identical. Heterometal derivatives incomplete cubanes and linked cubanes are also known. While the structure is often distorted from a simple cube the term 'cubane' is often used for convenience.The chromium hydride cubane (4) was obtained46 as in Scheme 1. The Cr-Cr distances are long (2.715A) compared with 2.642A for (5) and 2.263A for (6). The decrease from (5) to (6) is expected for the change from four-electron chloro bridges to the two-electron methyl bridges and the stronger Cr-Cr bonding is consistent with the reduction in pefffrom 2.0,~~ to 0.9 pB.Compound (4) exhibits almost ideal Curie-type paramagnetism with peff= 2.83~~ down to 15K. While structural parameters for hydrogen are often uncertain from X-ray diffraction studies there is sufficient evidence to point to hydride ligands capping the faces of the chromium tetrahedron. (5) (R = Me Bun,CHzSiMe3) ,SP* (6) R = Me Scheme 1 A central cubic structure (7) of alternating molybdenum and oxygen atoms was found4' in [(Mo0,Cr(bispictn)),][C10,],.The configuration around chromium is alternately A and A. The minor product [Mo,0,(p3-O),(OSiMe3),(NHMe,),] from the co-condensation of MOO and Me,SiNMe a cubane structure with molybdenum(v) supported by monodentate ligands only. 46 R. A. Heintz B. S. Haggerty H. Wan A. L. Rheingold and K. H. Theopold. At~qew.Chern. Int. Ed. Enql.. 1992 31 1077. 47 J. Glerup A. Hazell and K. Michelsen Actu Chern. Scand. 1991 45. 1025. 4x G.S. Kim D. A. Keszler and C. W. DeKock. Inorg. Chem. 1991. 30 574. 132 H. Sloan (7) L = tetradentatebispictii The kinetics of the substitution by thiocyanate at molybdenum in the cubane [Mo~'S,(H,O),,]~+ showed4' two consecutive reaction steps an equilibrium for substitution at each of the four Mo centres by NCS- followed by an isomerization.For the mixed-valence cation [Mo,S,(H,O) ,I5+ ,two concurrent substitutions occur having statistical factors consistent with the presence of three Mo centres different from the fourth. Kinetic studies provide evidence for electron distribution corresponding to three Mo"' and one Mo" centres. An extensive series of Mo-S cubanes has been prepared5' with various mono-anionic dithiolate ligands [R,NCS, (RO),PS, ROCS, RSCS,] providing the sulfur atoms of the cube. The relative ease of reduction of these cubanes is RSCS > ROCS > (RO),PS > R,NCS,. Facile preparative techniques and crystal structures are reported5 for the incom- plete cubanes [M3(p3-S)(p-S),(H,0)9]4+ (M = Mo W) and derivatives with other ligands (NCS- tridentate Hnta) in place of water.Treatment of the trinuclear incomplete cubanes [MO~S~O~-,,(H,O)~]~'= 2 3 4) with borohydride (8 n caused5 replacement of the p2-S by p2-0,but further reaction with (8 n = 1) resulted in loss of the trinuclear structure rather than replacement of the p3-S by oxygen. The distorted cubane [WV(Ntol)(S,P(OEt),)(p3-S)] (9) has53 the tetrameric structure in the solid and this is also the dominant form in solution. The visible spectra are consistent with a dissociative equilibrium (more favourable for the W complex than for Mo) further evidence for which was obtained by the formation of a mixed cubane core [Mo2W2S4]on mixing solutions of the tungsten and molybdenum analogues.The mixed Mo-W incomplete cubanes [M,M'S,(H,0)9](ptolS03),~9H,0 (M = Mo M' = W; M = W M' = Mo) have the molybdenum and tungsten atoms statistically di~ordered;~~ they are both isomorphous with the analogous all-molybdenum (M = M' = Mo) or all-tungsten (M = M' = W) analogues. 49 Y. J. Li M. Nasreldin M. Hurnzres and A. G. Sykes Inorg. Chem.. 1992 31 301 1. 50 C. L. Coyle K. A. Eriksen S. Farina J. Francis Y. Gea M. A. Greaney P.J. Guzi. T. R. Halbert H. H. Murray and E.I. Stiefel Inorg. Chim. Acta. 1991 198-200 565. 51 T. Shibahara M. Yarnasaki. G. Sakane K. Minarni T. Yabuki and A. Ichimura Inorg. Chem. 1992,31 640. 52 Q.-T. Liu J. Lu and A.G.Sykes. Inory. Chrm. Actu. 1991 19&200. 623. 53 M.L. Sarnpson J. F. Richardson and M. E. Noble. Inorg. Chem.. 1992 31 2726. 54 T. Shibahara and M. Yarnasaki. Inorg. Chem. 1991 30. 1687. Cr Mo and W [Groupsp-tolyl and (EtO),PS not shown for clarity] The mixed-metal cubane [MO~MS,(H~O),~]~+ Fe Ni) reacted55 with Cu2+ (M = in aqueous media to give replacement of M by Cu. The Mo3S part of the central moiety is unchanged. Reaction of the incomplete cubane [Mo~S,(H,O),]~+ (10)with metallic cobalt gave56 a double cubane [(H,0),Mo3S,CoCoS,Mo,(H,0),1 [ptolSO3].l8H,O in which two Mo,S,Co moieties are joined through two Co-S bonds. Reaction with Hg gave [(H,0),Mo,S,HgS,Mo3(H20),][pto1S0,]-20H20 in which the mercury atom is sandwiched between two Mo3S4 units through six Hg-S bonds.A similar reaction with Ni gave5' [Mo3NiS,(H,0),,][pto1S0,1 .7H20 with a very low magnetic moment. This was reacted further with nitriloacetate in aqueous KOH to give [Mo3NiS,(Hnta)(nta),C1l5 -. In [W,Cu,S,(SCH,CH,S),(PPh3)2],the tungsten atoms are5* five-coordinate and bound to the sulfur atoms of the cubane moiety and chelating dithiolato ligand. The distorted cubane structure of [{WCU,S,CI)(S)(PP~,)~] was found to have5 tungsten tetrahedrally coordinated to the four S atoms. Similar tetrahedral WOS moieties The occur6* in [( WCU,S~(S,COE~))(O)(PP~~)~].related selenium cubane [{ WCu,Se3C1)(Se)(PPh,),1 has been prepared61 and used to give complexes contain- ing bridging WSe ligands. Heptanuclear [PPh,] ,[ W ,Cu,O,S,(S,CNEt ,),]-dmf has6' an anion containing two defective cubane units OWS3Cu2 and OWS,Cu, linked by bridging S,CNEt2 ligands and weak Cu-S bonds.5 Quadruple Metal-Metal Bonds Dinuclear complexes of general form [M2X,] with an M-M quadruple bond show a cubic arrangement of ligands. The possible motion of the M-M unit within the cube has been considered6 by means of Fenske-Hall-type molecular orbital calculations. Similar calculations were made for octahedral or [M2X6] complexes where the change '' T. Shibahara T. Asano and G. Sakane Polyhedron 1991. 10 2351. s6 T. Shihahara H. Akashi M. Yamasaki and K. Hashimoto Chem. Lett. 1991 689. " T. Shibahara M. Yarnasaki H. Akashi and T. Katayama. Inorg. Chem.. 1991. 30 2693. '' N. Zhu R. Wu and X.Wu Acta Crystallogr. Sect. C 1991 47 1537. '')N. Zhu J. Wu and X. Wu. Acta Crystullogr. Sect. C. 1991 47 856. S. Du N. Zhu P. Chen and X. Wu. Angew. Chern. Int. Ed. Enyl.. 1992. 31 1085. 61 C.C. Christuk M.A. Ansari. and J.A. Ibers Angew. Chem. Int. Ed. Engl.. 1992 31 1477. 62 R. Cao X. Lei. and H. Liu Actu Crystallogr. Secr. C. 1991. 47. 876. 63 R. H. Cayton and M. H. Chisholm Inory. Chem.. 1991 30. 1422. 134 H. Sloun does not appear to be of sufficiently low energy to be operative as an isomerization step though it is not disallowed on symmetry grounds. The Cr-Cr quadruple bond in [Cr,(p-bet),(H,O),] has6 symmetric bridging zwitterionic betaine ligands and weakly bound terminal aquo groups. The tempera- ture-dependent partial paramagnetism of [Cr,(O,CR),L,] (R = Me CF,; L = MeOH H,O py MeCN) and related compounds has been shown65 to reflect a distribution of electrons between a ground state with S = 0 and a low-lying state with S = 1.For R = Me the singlet-triplet separation varies inversely with the Cr-Cr distance as L is changed. The corresponding carbamato compounds (R = NEt, L = NHEt,) show smaller singlet-triplet gaps for similar Cr-Cr distances possibly due to different interaction with the 6 orbital. The complexes [Mo,X,(PR,),] (X = F R = Me, Me,Ph) prepared66 by reacting [Mo,Me,(PR,),] with Olah’s reagent (py-xHF) have a Mo core disordered in three directions within a symmetric cube of the eight ligands. Correlations were found between 6-6* transitions ligand-to-metal charge transfer bands Mo-X distances and NMR shifts for many known compounds with X = F Cl Br or I.Assignments of the far IR frequencies have been made67 for a number of [Mo,X,L,] complexes [X = C1 Br I; L = AsMe, PR (R = Me Et Pr Bu)] with the aid of a vector addition model. Complications arise from the presence of internal ligand deformation modes in the same spectral region. The determination of the energy separations from the magnetic susceptibility of the solid has been widely used over a wide temperature range and with considerable accuracy. The alternative method via the 31P chemical shifts is reported6* for quadruply-bonded complexes of type [Mo,Cl,(L-L),] [L-L = dmpe depe dppe dppee dppp (PMe,),]. The barrier to rotation of the Mo-Mo unit within the cubic array of the ligands was determined to be 9.9kcal/mole.[Mo,(pyphos),] (11) has69 Mo-Mo 2.103A indicating a bond order of four. Reaction of (1 1) with [Mo(CO),(NCMe),] [PdCl,(NCPh),] or [PtBr,(cod)] gave (12 a,b,c). Complexes (12 b,c) exhibit intense absorptions at 645 and 660 nm respectively suggesting dative Mo -+ M (M = Pd Pt) bonding. The reaction of the molybdenum(I1) complex [Mo,(O,CCF,),] with anthraquinone (AQ) in benzene gave” achain polymer [(Mo,(O,CCF,),~AQ},]. X-Ray and spectral studies show two differently bonded AQ moieties linking the dinuclear molybdenum entities. However the interaction has little significant effect on the electronic structure of the Mo core. Reaction of [Mo,(B,CR) (R = Me Ph) with [NRk],[WS,] (R‘ = Et Pr) gave71 thecomplex [NR4]2[Mo2(0,CR),(WS4)2] in which the quadruply bonded Mo-Mo is bridged by all four ligands; pairs of like ligands are mutually trans.There is some lengthening of the Mo-Mo bond compared with the starting complex. The WS moieties in the benzoate complex (R = Ph) are tilted so that one of the non-ligating sulfur atoms is directed towards the aromatic ring of the adjacent benzoate ligand. 64 W. Clegg B. P. Straughan and A. R. Yusoff Acru Crystullogr. Sect. C 1992 48. 1896. ‘’ F.A. Cotton H. Chen L. M. Daniels and X. Feng J. Am. Chem. Soc. 1992 114 8980. “ F. A. Cotton and K. J. Wiesinger Inorg. Chem. 1992 31 920. ‘’ M. D. Hopkins V. M. Miskowski. P. M. Killough A. P. Sattelberger W. H. Woodruff. and H. B. Gray Inorq. Chem. 1992 31 5368.‘’ F. A. Cotton J. L. Eglin B. Hong and C. A. James J. Am. Chem. Soc,.. 1992 114 4915. 69 K. Mashima H. Nakano. T. Mori H. Takaya and A. Nakamura Chem. Lett. 1992 185. ’” M. Handa H. Sono K. Kasamatsu K. Kasuga M. Mikuriya and S. Ikenoue Chem. Left. 1992 453. ” M. A. Greaney and E. I. Stiefel. J. Chrm. Six. Chem. C’ommun.. 1992 1679. Cr Mo and W 135 0-N-P O-N-P P- N- 0 P- N- 0 (11j P-N-O = pyphos (12) a ML = Mo(CO),; b ML = PdCl,; c ML,=PdBrz Reaction of [Mo,Me,(PMe,),] and C,F,OH gave72 [Mo,(OC,H,),(PMe3),] with the evolution of methane. This is the first example of a 1,2,7,8 isomer with unidentate ligands for the square prismatic structure [positions labelled as in (13)] though it may not be the thermodynamically most stable isomer due to the rapid precipitation of the product.[Mo,(O,CCF,),] reacted7 readily with bipy in MeCN giving the salt [Mo2(p-02CCF3)2(bipy),][02CCF,I whose structure was confirmed by X-ray diffraction. The IR and NMR spectra confirmed the presence of both ionic and ligated tri- fluoroacetate groups but temperature and solvent dependent isomerization occurred. The independent preparation of [M0,(q~-O,CCF,),(bipy)~]-2Me,C0 showed this to be the isomerization product having a very short unsupported Mo-Mo quadruple bond (2.077A). The isomerization also occurred photochemically. Binuclear compounds with weakly coordinated ligands are of interest for catalysis and preparative studies. The highly reactive salt [Mo,(NCM~),(UX-NCM~)~][BF,I -2MeCN was prepared7 from [Mo,(OAc),] and [OEt,][BF,] in acetonitrile; the centrosymmetric cation has linear Mo-N-C groupings except at the axial positions where the bent Mo-N-C angles appear to arise from interactions with the solvate molecules.The Mo-Mo distance is unusually long (2.187 A) for a quadruple bond. 'H NMR spectroscopy shows labile acetonitrile ligands undergoing rapid exchange with solvent. A comparison of the structures of [M,(dfm),] (M = Cr W) with those of the 72 F. A. Cotton and K. J. Wiesinger. Inorg. Chem. 1991 30 750. 73 J. H. Matonic S.-J. Chen. S. P. Perlepes K. R. Dunbar and G. Christou J. Am. Chem. Soc.. 1991 113 8169. 74 F.A. Cotton and K. J. Wiesinger Inory. Chrrn. 1991 30 871. 136 H. Sloan molybdenum analogue and other similar quadruply bonded complexes that the M-M bond lengths are insensitive to the use of more basic chelating ligands unlike the situation for Ru" 0s"'.Several quadruply-bonded heterobimetallic complexes [MoWCl,(L-L),] (L-L = bidentate phosphine) have been prepared.76 These gen- erally show the increased sensitivity towards oxidation typical of the homobimetallic tungsten analogues compared with the molybdenum analogues. However there is reduced reactivity towards alcohols comparable with the molybdenum analogues. Some of these complexes have chelating (designated 2) as opposed to bridging (designated p) diphosphines. The diamagnetic anisotropy of the Mo-W quadruple bond was essentially the same as that for the Mo-Mo bond. 6 Triple Metal-Metal Bonds The molybdenum-molybdenum triple bond is bridged77 by two (2S,3S)-2,3-bis(dipheny1phosphino)butane ligands in the symmetrical complex p-[Mo,(NCS),(dppb),]MeNO where the thiocyanate groups are N-coordinated.Reaction of symmetric [W,Cl,(NMe,),] with LiPR (R = Et Cy Bu' Ph SiMe, ptol p-C,H,F) at temperatures below 0°C resulted in substitution of the chloro ligands by PR,78 with retention of the W-W triple bond. These complexes occur in anti and gauche forms. On warming to over O'C or by direct reaction at higher temperatures further isomers are formed with bridging PR ligands. The 31P NMR spectra showed chemical shifts in the order anti < gauche < bridged. Crystal structure determinations of several of these comFounds gave W-W bond lengths consistent with the retention of the triple bond.A labile leaving group the trifluoromethanesulfonate ligand in [W,-(NMe,),(O,SCF,),] was introduced79 by reacting [W,(NMe,),] with Me,SiO,SCF,. This product has a symmetric anti-W,O,N core and reacted with PMe to give [W,(NMe,),(03SCF3)3(PMe3)2]. The latter contains roughly square planar WON,P and W0,NP units connected by a tungsten-tungsten triple bond in a staggered conformation. The W-0 and W-N distances C2.205 8 and 2.008 (ave) respectively] in the WON,P moiety are longer than those in the W0,NP moiety (average 2.13 8 and 1.928 respectively). The reaction of [W,(OR),] (14 R = SiMe,Bu') and NO in the presence of pyridine in a hydrocarbon solvent resulted inEo cleavage of the W-W triple bond and formation of a [W(NO)(OR),(py),] at low temperature (-72 "C) a reaction analogous to that of the complex (14 R = Bu').At higher temperatures however the NO bond of the siloxy complex cleaved giving CW(O)(OR),(PY,l and CW,(O),(OR),(PY),I* 7 Face- and Edge-sharing Bioctahedral Complexes The formation of binuclear complexes raises the question of the existence and order of l5 F.A. Cotton and T. Ren J. Am. Chem. Soc.. 1992 114 2231. 76 F. A. Cotton and C. A. James Inorg. Chem. 1992. 31 5298. 77 A. A. Aitchison L. J. Farrugia and R. D. Peacock Acta Crystallogr.,Sect. C 1991 47. 2556. l8 W. E. Buhro M. H. Chisholm. K. Folting J. C. Huffman J. D. Martin,and W. E. Streib J. Am. Chem. SOC. 1992 114 557. 79 M. H. Chrisholm K. S. Kramer J. D. Martin J.C. Huffman E.B. Lobkovsky and W. E. Streib Inorg. Chem. 1992 31 4469. '"M. H. Chisholm. C.M. Cook. K. Folting and W. E. Streib Inorg. Chim. Acta 1992 198-200 63. cr Mo and w 137 direct metal-metal bonding. The properties of these compounds often depend subtly on the electronic interaction between the metal centres whether through the direct link or through the bridging ligands. The mer configuration in solution of octahedral [MoX,L,] (X = Cl Br I; L = PMe, PEt, PMe,Ph) was established” from NMR spectroscopy. For the chloro complexes and the corresponding face-sharing [Mo,CI,L,] and the edge- sharing [Mo,Cl,L,] binuclear species the relative stability sequence face-sharing < edge-sharing << monomer holds in a phosphine-rich environment. The edge-sharing bioctahedral heterobimetallic complex [MoWCl,(p-CI)(p-H)(p- dppm),].2thf.C,H6 is formeds2 by the reaction of [MoWCl,(PMePh,),] with dppm.The complex contains trans dppm ligands. The Mo-W distance is consistent with multiple bonding and is unusually short for a (111)-(III) core. The oxidative addition of Y (Y = C1 Br I) to the quadruply bonded [Mo,X,(dppm),] (X = C1 Br I) forms nine edge-sharing bioctahedral complexes [Mo,X,Y,(dppm),]. Their structural and magnetic susceptibility properties indicated8 that both direct M-M coupling and indirect coupling across the p-X atoms occurs. Addition of lithium powder to cis-[WF,(OMe),] followed by excess NaOMe in thf gave84 edge-sharing bioctahed- ral [W,(OMe),,] where the W-W distance is consistent with single bonding.The use of resonance patterns in the ‘H NMR spectra of face- and edge-sharing bioctahedral complexes [Mo,Cl,L,] and [Mo,Cl,L,-,,L’], (L,L’ = phosphines) has been developed8’ to provide precise information on chemical identity and stereochem- istry. The mechanism of the transformation of edge- to face-sharing compounds has been studied. A large effect on the magnetic properties of the edge-sharing compounds is observed on quite simple substitutional interchange of PMe and PEt,. A logarithmic relationship has been determined8 between the spin exchange coupling constant and the metal-metal distance mainly for chromium face-sharing octahedral binuclear complexes. The bridging ligands include 0x0 hydroxo alkoxo and halo groups. The reaction of [W,(NMe,),] and ROH (R = cyclopentyl) in hexane initially formed [W,(OR),(NHMe,),] which converted8’ on standing to [W,(p-H)(p-OR),(OR),(NHMe,)] (15).This has a confacial bioctahedral structure; the position of the hydrido bridge is inferred to be trans to the NHMe ligand to form the (OOH) common face. The dimethylamine is readily replaced by PMe and in solution (15) is in equilibrium with [W,H(OR)J and free amine or phosphine. The face-sharing bioctahedral complexes [Mo,X,(PMe,Ph),] (X = Br I) were obtaineds8 by reacting [MoX,(thf),] with PMe,Ph in a 2 :3 ratio in refluxing toluene. Like the known complex with X = C1 they have three bridging halogen atoms; the R. Poli and H.D. Mui Inorg. Chem. 1991 30 65. F. A. Cotton C. A. James and R. L. Luck Inory.Chern. 1991 30 4370. 83 F. A. Cotton L. M. Daniels K. R. Dunbar L. R. Falvello C. J. O’Connor and A. C. Price Inory. Chrm . 1991 30 2509. 84 J. C. Bryan,D. R. Wheeler D. L. Clark J. C. Huffman,and A. P. Sattelberger,J. Am. Chem.Soc.. 1991.113 3184. ” R. Poli and J.C. Gordon J. Am. Chem. Soc. 1992 114 6723. n6 A. Niemann U. Bossek K. Wieghardt C. Butzlaff. A. X.Trautwein and B. Nuber Angrw. Chem.,Int. Ed. Engi.. 1992 31 311. ’’ S.T.Chacon M. H. Chisholm K. Folting M. J. Hampden-Smith and J. C. Huffman Inory. Chrm. 1991 30 3122. ** J.C. Gordon. H.D. Mui R. Poli and K.J. Ahmed Polyhedron 1991 10 1667. 138 H. Sloan other ligands were shared so that two halogen atoms and one phosphine are at one metal centre while one halogen and two phosphines are bound to the other.The inter-metal distance increases in the order CI < Br < I and the paramagnetism increases similarly as shown by solid-state magnetic susceptibility measurements and by solution NMR spectroscopy. The latter also showed an equilibrium between the anti and gauche forms. Reduction of WCl with Na/Hg (or NaBEt,H) followed by treatment with 1 or 1.5 equivalents of PMe2Ph gaves9 edge-sharing [W2C16(PMe2Ph),] and face-sharing [W2C16(PMe2Ph)3] respectively. Similar reactions with WBr gave the first bromo- bridged face-sharing complexes [W,Br,(PR,),] (R3 = Me2Ph Me,). The W-W bond distances of these four complexes are 2.6950,2.4433,2.4768 and 2.4496 8 respectively indicating strong metal-metal bonding. They are the shortest such bonds in neutral halogen bridged complexes so far described.8 Triangular Cluster Complexes Triangular clusters are known with 6 7 8 and 9 valence electrons involved in the metal-metal bonding and with combinations of doubly and triply bridging ligands usually oxygen sulfur or halogen donors. SCF-X,-SW calculations have been madeg0 for various trinuclear molybdenum and tungsten cluster compounds of the form [M3XI3] (X = one or two of 0,S Cl). Salts of [M~,(p~-s)(p,-s,),X~]~- (X = C1 Br I) reacted” with KSeCN in MeCN to form [Mo3(p3-S)(p2-SSe)3(Ncs)6]2 where substitution of sulfur by selenium has occurred only at the equatorial S atoms. The cluster complex [MO~(~~-S)~(~- S),(PMe,),] preparedg2 by treatment of [NH,],[MO,S,,] with excess PMe in thf has a three-fold axis of symmetry through the centre of the Mo triangle.The subtle Jahn-Teller effects that may occur in such eight-electron cluster complexes is emphasized by the contrasting isosceles triangular metal moieties of [Mo~(,u~--(shorter base) and [cr,(,~~-S)~(p-S s)2(,kcI)3c16]3 j,(dppe),] (longer base). The reaction of excess PEt with [Mo,S,Cl,] [Mo,S,Br,] or [W,S,Br,] gave’ [Mo3 (p3-s )(p-s)3c14(PEt3)3 (H20)21‘OPEt 3 [Mo 3 (p3-S)b-sj 3Br4(PEt 3 )3 (OPEtzH) (H 0)] .2 t h f or [W,(p,-S)(p-S) B r ,(P E t ) (0P E t H)(H 0)] .2 t h f re spec t ivel y . These have similar structures though the three metal atoms in each compound have a different coordination sphere. It is proposed that the OPEt2H ligand arises by oxidation of PEt, coordination hydrogen abstraction by a metal atom from an ethyl group and subsequent elimination of ethene and transfer of the hydrogen to phosphorus (Scheme 2).Compounds containing the ions [M 3(p3-O)(p-Cl)3(p- OAc),Cl,]-(M = Mo W) were prepared9 by the reaction of MoC13.3H20 or [NEt,],[W,CI,] with excess Ac20 and AcOH or 1 M hydrochloric acid respectively. While six-electron triangular clusters are well known these are eight-electron clusters of which there are few examples. The relative stabilities of the different oxidation levels 89 F. A. Cotton and S. K. Mandal Inorg. Chrm. 1992 31,1267. F.A. Cotton and X. Feng Inorg. Chem.. 1991 30 3666. 91 V. P. Fedin M. N. Sokolov. V. Ye. Fedorov D. S. Yufit and Yu.T. Struchkov Inorg. Chim. Actu 1991 179 35.92 K. Tsuge S. Yajima H. Imoto and T. Saito J. Am. Chem. Soc. 1992 114 7910. 93 F.A. Cotton P. A. Kibala and C. S. Miertschin Inorq. Chrm. 1991. 30 548. 94 F. A. Cotton M. Shang and Z. S. Sun J. Am. Chem. Soc. 1991 113 3007. Cr Mo aiid W are strongly affected by the bridging ligands. Chloro rather than 0x0 groups favour eight- rather than six-electron clusters and the redox behaviour of Mo/W homologues can be remarkably different. When Mo is not bound to a phosphine ligand in the nine-electron clusters [MO~(~~-O)(~-C~),(~-OAC)~C~~(PR~)~ -,,I' -'(n = 1-3) the Mo-Mo bond lengths95 are longer than in the eight-electron compounds mentioned above; the other Mo-Mo bonds are similar in length. The Mo-Cltermi,, bond lengths become shorter with increasing value of n.M -OPEt -M-OPEt + GH, I CH2-CH2 H Scheme 2 The reaction of nitrous oxide (as an oxygen source) with [W,(OR),] (R = Bu') in pentane at -15 ''C gave9 the triangular six-electron cluster [w,o,(oR),] with no capping ligand; one of the W-W bonds has no bridging 0x0 ligand. NMR spectroscopy indicates that each of the tungsten atoms has a different coordination sphere. On carrying out the reaction at higher temperatures or on warming the product disproportionation occurs to [W2(0R),] and [WO,(OR),]. 9 Hydride and Dihydrogen Complexes Conclusive evidence for the existence ofpu,-H in [MO~(~~-I)(~~-H)(~-I)~I~L~] has been provided9' by the observation of 1 3 3 1 quartets in the 'H NMR spectrum. Variable temperature ' and ,' P CP/MAS NMR spectroscopy of the nine-coordinate complex [WH,(PMe,),] showed9 it has a tricapped trigonal prismatic structure.Two of the phosphine ligands are in eclipsed but inequivalent prismatic sites and the third caps the prismatic face opposite the other two. Ligand functionality interchange between the phosphine sites occurred above 340 K. The formally 14-electron complexes [MH(SC,H,R,),(PMe,Ph),] (M = Mo W; R = Me Prl) have99 a distorted trigonal bipyramidal geometry with respect to the non-hydride ligands; the phosphines are essentially trans in the apical positions. NMR studies of the hydrides and their deuteride analogues show low-field hydride shifts. There is a large coupling to one of the phosphorus donors indicating an asymmetric location of the hydride ligand with respect to the phosphine ligands.Several polyhydride derivatives of tungsten and molybdenum are reported,' O0 including [M(n-crown-n')][WH5(PMe,),] (M = K n = 18 n' = 6; M = Na n = 15 n' = 5)and [(W(PMe,),H,Lii,] where crystal structure and spectroscopic data show considerable covalent bonding W-H . . . M for the lithium sodium and potassium compounds. '' F.A. Cotton M. Shang. and Z.S. Sun J. Am. Chem. Soc. 1991 113 6917. Yh M. H. Chisholm C. M. Cook and K. Folting J. Am. Chem. Soc.. 1992 114. 2721. A. Burini F.A. Cotton and J. Czuchajowska Polyhedron. 1991. 10. 2145. YH S. J. Heyes M. L. H. Green and C. M. Dobson. Inorg. Chrm. 1991 30 1930. YY T. E. Burrow. A. Hills D. L. Hughes J. D Lane. R. H. Morris and R.L. Richards. J. Chum. Soc. Dalton Trans.. 1991 1813. loo A. Berry M.L. H. Green J.A. Bandy. and K. Prout. J. Chun. Soc. Dnlron 7rans.. 1991 2185. 140 H. Sloan Reaction of the basic hydrides trans,trans-[WH(CO),(NO)(PR,),] (R = Me Et Ph OPr') with the Lewis acidic BH,-L (L = thf or SMe,) gave"' air sensitive trans-[W(q2-BH,)(CO)(NO)(PR,),] as the main product; the more acidic hydrides (R = OMe OPh) did not give such a borohydride. In general these compounds are unstable with respect to elimination of BH,-PR and were characterized by spectral methods. However a structural study of the complex (R = Me) was possible showing a distorted octahedron. trans,trans-[WH(CO),(NO)(PMe,),] reacted" readily with pyridin-2-yl aldehydes and ketones. Insertion of the C=O bond into the W-H bond led to the formation of tungsten alkoxides and rapid extrusion of CO followed to give 0,N-chelates.The barrier to rotation of dihydrogen in [Cr(CO),(PCy,),(q'-H,)] has been foundlo3 to be 1.5 kcal/mol by an inelastic neutron scattering method which also provided unambiguous proof of the dihydrogen binding. There is a contrast in the solid and solution stabilities of this complex where loss of hydrogen in solution is assisted by the agostic interaction of a hydrogen in the 2-position of a cyclohexyl substituent. The reaction of arachno-[B,H,,]- with [M"I,(CO),L,] (M = Mo W; L = PPh, PPh,Me PPhMe,) gavelo4 6,6,6,6-(CO),(PR3),,-6-M-B9H1 [M = Mo x = y = 2 (known previously); M = W x = 3 y = 13. The tungsten compound has structure (16).(16) Each boron atom also bears an exo-hydrogen atom 10 Carbon-donor Ligands In an unusual redox elimination reaction (17) loseslo5 CO and ethylene to give the Mo'" complex (18). Such high-valent carbonyl complexes are rare. IR and NMR spectroscopy show symmetrically oriented dithiolate ligands with cis carbonyl groups. Similar elimination of CO and ethylene from the PPh derivative (19) gave the corresponding complex (20). The high frequency CO absorption in the IR spectrum and the observed Mo-CO distance are consistent with bonding to an electron-deficient Mo centre. Protonation of [W(CO),(PCy,),] with HBF;OEt in toluene gavelo6 A.A.H.van der Zeijden. V. Shklover and H.Berke Inory. Chem. 1991 30 4393. A.A.H. van der Zeijden and H.Berke. Helv. Chim. Acta 1992 75 513. J. Eckert G. J. Kubas and R. P. White Inorg. Chrm. 1992 31 1550. '04 P. K. Baker M. A. Beckett and L. M. Severs. Polyhedron. 1991 10. 1663. 10s D. Sellmann F. Grasser F. Knoch. and M. Moll Anyew. Chem. Int. Ed. Engl.. 1991 30 131 1. L. S. Van Der Sluys K.A. Kubat-Martin G.J. Kubas and K. G. Caulton. Inory. Chem. 1991 30. 306. Cr Mo and W a b + C2H4 + CO (17) R=CO (18) R= CO (19) R = PPh3 (20) R = PPh3 a R = CO 25 "C vacuum 15 days b R = PPh, 65"C thf 75 min [WH(CO),(BF,)(PCy,),] (21). X-Ray diffraction shows disorder in the oxygen atom of the CO group trans to the BF ligand; the W-C-0 linkage is definitely non-linear. The 'H and 31PNMR spectra show inequivalent phosphine ligands; disorder in the hydride position is also proposed as shown.The very long W-W bond (3.288 A) in [W,(CO),Cp;] has' O7 some support from two semi-bridging carbonyl groups with the W-C-0 angle at 170.4'. CY3 (21) O' H' and 02,H2 represent alternative positions for the oxygen of the carbonyl and the hydride ligands. Mononuclear compounds containing the cylindrically symmetrical but electroni- cally disparate carbonyl r-acid and 0x0 r-base ligands are rare. Oxidation of [NE~,][W(CO),{HB(M~,~Z)~)] by iodine or bromine in CH,CI or MeCN gave [WX(CO),(HB(Me,pz),)] (X = I Br) which may be further oxidized"' by dioxygen in refluxing toluene or hot MeCN to give [WXO(CO){HB(Me,pz),>]. The latter has an unusually low-field 13C signal near 280ppm assigned to the CO ligand.Further oxidation to the more thermodynamically stable cis-dioxo complex lo' A. L. Rheingold and J. R. Harper Acra Crpralloqr. Srcr. C. 1991 47 184. 10R S.G.Feng. L. Luan P. White M.S. Brookhart J. L. Templeton and C. G. Young lnorq.Chrm. 1991.30 2582. 142 H. Sloan [WO,X{HB(Me,pz),)] occurs. The intermediate iodotricarbonyl also reacted with aniline to form the nitrene complex [W(NPh)I(CO){ HB(Me,pz),)] for which vco and the 13C chemical shift for the carbonyl carbon indicate the greater electron density available for back-bonding compared with the 0x0 analogue. Evidence for a bent nitrene intermediate was obtained"' from the reaction offac-[Mo(CO),(NCMe),L1 [L = PPh, MeCN P(OMe,), P(OEt,),] and 8-azidoquinoline.In particular the reaction when L = PPh gave as major products (22) and (23). (22) z= co (23) Z = PPh3 Attempts to prepare [Cr(CO),(CNH)] (24)showed"' that the hydrogen isocyanide ligand forms strong hydrogen bonds to cyclic ethers and crown ethers. The adduct with thf for example is sufficiently stable to be sublimed. Crystallization from ether-layered CH,CI solutions of equimolar amounts of (24) and [ER,][Cr(CO),(CN)] (ER = NEt or AsPh,) gave the [AHA]- type ion (25); a strong possibly symmetric hydrogen bond is shown by single I3C NMR signals for each of CN COcis and COfrans and band deficient IR and Raman spectra. X-Ray structure analysis supports a strong hydrogen bond with an N(H)..-N distance of 2.569A as does the "N-CPMAS- NMR spectrum of (25 ER = AsPh,) which shows only a single line for the equivalent N atoms.By contrast the "N-CPMAS-NMR spectrum of (25 ER = NEt,) gave two signals. The asymmetric complex [Cr(CO) {CNHNC)Fe(dppe)Cp] shows markedly different CN bands in the IR and different CN signals in the NMR spectra. 11 Carbon Dioxide and Carbonate Ligands The reaction of CO with cis-[Mo(N,),(PMe,),] in coordinating solvents gave" * the carbonyl-carbonate complexes [{Mo(~(,-~~,~~-CO,)(CO)(PM~,),}~] (26) and [Mo(CO,)(CO)(PMe,),] (27)derived from the reductive disproportionation of CO,. J.L. Fourquet M. Leblanc A. Saravanamuthu M. R. M. Bruce and A. E. Bruce Inorg. Churn.. 1991,30 3241. 'lo E. Bar J. Fuchs D. Rieger F. Aguilar-Parrilla. H.-H. Limbach.and W. P. Fehlhammer Angrw. Chum.. In?. Ed. Engl. 1991 30 88. 'I' R. Alvarez J. L. Atwood E. Carmona P.J. Perez M. L. Poveda and R. D. Rogers Inorq. Chem. 1991.30 1493 Cr Mo and W Ether or thf as solvent led to the preferential formation of (26)while acetone gave (27). The two products interconvert readily by association or dissociation of PMe, and solution stability is strongly solvent dependent. Further reaction with chelating phosphines gave [Mo(CO,)(CO)(P-P)(PMe,),] (P-P = dmpe dmpm) and [Mo(CO,)(CO)(dmpe),]. Both (26) and (27) react with water giving the Mo"-MoV complex (28) where the carbonate ligand is engaged in a novel type of bonding. (26) R= Me (27) R=Me Carbonate provides' l2 the sole link between the chromium(m) centres in a notably robust complex trans-[(Cr(NH,)(~yclam)),(p-CO,)]~', which is unaffected by hot 6M hydrochloric acid.There is antiferromagnetic coupling between the chromium centres. Excess methanol or NR,H [R = Me Et; R = (CH,), (CH,), (CH,),O(CH,),] reacted' ' with trans-[W(CO)(N,)(dppe),] under CO to give hydrido-carbonato [WH(y'-OCO,Me)(CO)(dppe),] or hydrido-carbamato complexes [WH(q2-O,CNR,)(CO)(y '-dppe)(y2-dppe)] respectively. The carbamato complex [R = (CH,),] treated with AIEt under CO gave trans-[W(CO)(CO,)(dppe),] with a C,O-coordinated y2-CO ligand. Detailed vibrational studies of trans-[Mo(CO,),(PMe,),] showed' ' that the CO ligands are bound side-on through carbon and one of the oxygen atoms. Exchange reactions between trans-[Mo(CO,),(PMe,),] with diphosphines (dmpm dmpe depe dppe) gave' '' mono-and di-chelated substitution of the simple phosphines.The existence of a number of conformations in solution depending on the variations in CO orientation was demonstrated and mechanisms for their interconversion considered. Complexes obtained by further substitution of PMe by RNC were also studied. E. Bang J. Eriksen J. Glerup L. Msnsted 0.Msnsted and H. Weihe Actu Chrm.Sund. 1991.45 367. 'I3 T. Ishida. T. Hayashi Y. Mizobe. and M. Hidai Inorg. Chern. 1992 31. 4481. I I4 C. Jegat M. Fouassier. and J. Mascetti Inory. Chrm. 1991. 30 1521. 'Is E. Carmona A. K. Hughes M. A. Muiioz. D. M. O'Hare P. J. Perez,and M.L. P0veda.J. Am. Chrm.Soc.. 1991 113. 9210. 144 H. Sloan 12 Silicon-donor Ligands Reaction of (29a) or (29b) with Na,[Cr(CO),] gave116 (30) with intramolecular base stabilization of the low-coordinate Si atom.In (30a) there is evidence from NMR spectroscopy for the alternating dynamical coordination of the NMe moieties to Si. The Cr-Si bond is noticeably short. The coordinated Si-N bond of (30a) is shorter than that in (29a). \ (29) a R = CH,NMq; (30) a R = CH,NMq; b,R=H b,R=H 13 Nitrogen-donor Ligands A correlation of calculated electron density shifts with the experimentally observed leaving groups in the photochemistry of chromium(Ii1)-ammine complexes has been observed.' l7 Ab initio calculations have been made' for [Cr(NH3)J3+ and a number of mono- and di-substituted chromium ammine complexes in a detailed analysis of their ligand field spectra.While spin-forbidden excitations are calculated to be too large results are generally in good agreement with experimental data. Pulsed photoacoustic microcalorimetry was used' ' to determine bond dissociation energies in [Cr(NH3),l3+ and [CrCl(NH3),]2f. A simple angular overlap model was in reasonable agreement with the results. Characteristic IR spectral properties have been identified' 2o for Cr-propylenediamine complexes. Linear correlations with Gutmann's acceptor numbers are found' ,' for the solvatochromic effects and solvent dependence of I3C NMR shifts of trans and cis-[Cr(N),(O),] type complexes. The p-cyano- bis[pentaamminechromium(r~~)] ion is antiferromagnetic. '22 One-electron oxidation of the anion [Cr(CO),(NO)] -with trityl hexafluorophos-phate gave'23 [Cr2(CO)a(NO)2] (31 )which has a molecular structure (Cr-Cr = 3.020 and 3.001 A two crystallographically independent molecules) analogous to that of 'I6 R.Probst C.Leis S. Gamper. E. Herdtweck. C. Zybill. and N. Auner. Anyrw. Chrm. Inr. Ed. Enyl. 1991. 30 1132. L. G. Vanquickenborne B. Coussens. D. Postelmans. A. Ceulemans and K. Pierloot. Inory. Chrm.. 1992 31 539. 'IxL.G. Vanquickenborne. B. Coussens D. Postelmans A. Ceulemans and K. Pierloot. Inory. Chrm. 1991. 30 2978. I") X. Song and J. F. Endicott. Inorc;. Chem.. 1991. 30. 2214. 12' Y. Sakabe and H. Ogura And. Sci, 1992. 8 63. ''I S. Kaizaki N. Koine. and N. Sakagami Bull. Chrm. Soc. Jpn.. 1991. 64. 2058. '22 J. Glerup and H. Weihe.Acru Chrm. Sund.. 1991 45 444. A. P. Masters M. Parvez and T. S. Sorensen. Curi. J. Chrm.. 1991 69 2136. Cr Mo and W [Mn,(CO),,] (Mn-Mn = 2.904 A) and isoelectronic [Cr,(C0)l,]2-. The NO groups are trans to Cr in both (31) and the anion [Cr,(CO),(NO)]- (Cr-Cr = 2.995A). [W(CO),(Benzo[c]cinnoline)] is octahedral with the benzocinnoline coordinated through one nitrogen atom only. The N-N bond order is significantly reduced contrasting with a benzocinnoline complex of iron where the N-N bond remains at its double bond length. Three-coordinate compounds of third row transition metals are rare. The first example for tungsten (32) prepared'24 as in Scheme 3 is diamagnetic and monomeric. It is stable in the solid form but decomposes slowly in solution.An X-ray structural determination showed it to be planar trigonal slightly distorted to a T-shape with relatively short W-N and W-0 bonds. Simple o-donors such as thfdo not bind to (32) but alkenes will do so readily. [(ButNH)2W(=NBu')2] + 2Bd3SiOH -[(Bu'$i0)2W(=NBut)2] + 2NBu'H2 benzene 3HC1 1IOOC 3.5 d1 - [(But3Si0)2W=NBu'] + MgCl Mg dust,Et2P [(Bu'~S~O),CI,W= NBu'] + [NBu'H3]CI 25"c,7 (32) Scheme 3 Fast time-resolved IR spectroscopy was to probe the metal to 4-cyanopyridine charge transfer excited state of [W(C0),(4-CNpy)]. On visible light irradiation the CO stretching vibrations shift to higher frequency confirming that in this excited state the metal centre is oxidized. The silylcobalt complexes [Co(CO),(SiR,R')] (R R' = Ph Me) reacted'26 with the dinitrogen complexes [M(N2),L4] (M = Mo W L = tertiary phosphine) to give the silyldiazenido complexes trans-[M(NNSiR,R' )L,(p-OC)Co(CO),] which were fur- ther converted to silylhydrazido(2 -) complexes such as [WX(NNHSiR,R' )(dppe),] [Co(CO),] by treatment with HX (X = OH OMe Br).In the diazenido complex (M = Mo R = Ph R' = Me) Mo-N-N is linear and the angle N-N-Si is 152.2". The Mo-0 bond in the Mo-0-C-Co chain is long (2.25681) and the angle Mo-0-C is 164.9'. Dinitrogen complexes of Moo and Wo are known to react with strong acids to give ammonia or hydrazine or ammonia and hydrazine uia disproportionation of a hydrazido(2 -) complex. The presence of SnCl or GeI increasesI2' the formation of ammonia in such reactions and decreases the yield of nitrogen.One of the coordinated dinitrogen ligands in [W(N,),(dppe),] is protonated' 28 quantitatively at room temperature by the strongly acidic [Ru(q2-H2)(dtfpe)Cp]+in thf to give the hydrazido(2 -) complex [W(NNH,)F(dppe),][BF,]. 1 ,I-Diphenyl hydrazine reacted' 29 with [MoO,(acac),] in methanol to give 124 D. F. Eppley P.T. Wolczanski and G.D. Vanduyne Angew. Chem.. Int. Ed. Engl. 1991. 30. 584. I25 P. Glyn F. P. A. Johnson M. W. George. A. J. Lees and J. J. Turner Inorg. Chem. 1991. 30. 3543. 126 A.C. Street Y. Mizobe. F. Gotoh 1. Mega. H. Oshita. and M. Hidai Chem. Lett. 1991 383. T.A. George and B. B. Kaul. Inory. Chem. 1991. 30. 882; T. A. George M.A. Jackson and B. B. Kaul Polyhedron. 1991. 10 461. 1 ZX G. Jia R. H. Morris and C.T. Schweitzer Innrg. Chem. 1991 30. 593. I29 C. Bustos C. Manzur H. Gonzalez R. Schrebler D. Carrillo C. Bois. Y. Jeannin and P. Gouzerh Inorg. Chim. Acta 1991. 185 25. 146 H. Sloan [MoO(NNPh,)(acac),] (33) or [(MoO(NNPh,)(acac)(p-OR)),] (34 R = Me) de- pending on the temperature. Complex (33) reacted in refluxing ROH (R = Me Et Pr) to give alkoxy-bridged (34). The geometry of the hydrazido(2 -) ligand is consistent with extensive delocalization through the Mo-N-N unit. Similar compounds result- ed' ,'with 1-methyl-1-phenylhydrazine. Cyanamide reacted',' with trans-[M(N,),(dppe),] (M = Mo W) to give trans- [M(NCN),(dppe),] which has a near linear Mo-N-C-N system and an Mo-N bond length consistent with a bond order greater than one.The dehydrogenation of cyanamide does not occur with less electron-rich cationic centres. The 'H NMR spectrum of [M,(OEPh,),(NMe,),] (M = Mo W E = C; M = W E = Si) showed13* a temperature-dependent mixture of anti and guuche forms. The structures are exclusively anti for molybdenum and gauche for tungsten in the methoxide derivatives and anti for the tungsten-silicon complex. The tungsten atom of [NBu,][WCl,(Nptol)]- one of the products of the reaction of [NBu,][H,PW ,O,,] and [WCI,(Nptol)], is 0.43A out of the plane*33 of four chlorine atoms in the distorted octahedral structure. The W-N bond (1.43 A) is consistent with a double bond and the W-N-C bonds are almost linear. The other product the anion [W,(p-O)Cl,(Npt~l),]~-with the p-tolylimido groups cis to the bridging 0x0 ligand is slightly folded to separate the aryl groups; variations in the W-N distances are consistent with the possible trans effects present.Treatment of [( WCl,) ,(/I-NC,H,N-1,4)] obtained from WOCl and C,H,(NCO),-I ,4 with PMe,Ph gave' 34 [{WC1,(PMe,Ph),),(p-NC6H4N-I ,4)]. The linear n-bonded 1,4-phenylenediimido bridge joins the mer,trans-{ WCl,(PMe,Ph),) fragments in an eclipsed conformation. 14 Phosphorus-donor Ligands Phosphorus reacts'35 with WO to give a mixture of WP WP, WPO, and the novel WP,O,. The compounds are readily separated in pure form by chemical vapour transport reactions. Heating solutions of the pentaphosphacyclopentadienyl anion P; in dme with [M(CO),(NCR),] or [M(CO),] (M = Cr Mo W) gave', the first mixed carbonyl(pentaphosphacyclopentadieny1)metal complexes [M(CO),(q5-P,)] -.The tungsten complex shows a remarkably small 13C-'83W coupling in the NMR spectrum; the IR spectrum shows the two CO absorption pattern typical of local C,, symmetry. The tungsten complex reacts with SiClMe, giving [W(SiMe,)(CO)(q'- P,)] where the 'H NMR signal of SiMe is similar to that in the corresponding cyclopentadienyl complex. The isomorphous and isostructural [M(CO),(dppb)] (M = Cr W and the previously reported M = Mo) show'37 the expected shorter bond lengths to chro- mium and the longer M-C bond for the rrans carbonyl groups. The chromium complex has a larger P-M-P angle. The structures of a series of bis(dipheny1phosphino)alkane 130 D. Carrillo F. Robert and P.Gouzerh Inorg. Chirn. Acru 1992. 197 209. 13' A. J. L. Pombiero Inorg. Chim. Acra 1991. 198 200 179. 132 M. H. Chisholm I. P. Parkin. J. C. Huffman. E. M. Lobkovsky. and K. Folting Polyhedron. 1991.10.2839. 133 Q. Chen D. McClinton and J. Zubieta Inorg. Chim. Acfa. 1992 195 163. 134 W. Clegg R. J. Errington D.C. R. Hockless. J. M. Kirk and C. Redshaw. Po/.phedron 1992 11. 381. 135 H. Mathis R. Glaum and R. Gruehn Acru Chem. Scand.. 1991. 45. 781. 136 M. Baudler and T. Etzbach Angew. Chem. Int. Ed. Engl.. 1991 30 580. 13' C.-H. Ueng and G.-Y. Shih Acta Crysfallogr.. Sect. C 1992 48 988. Cr Mo and W 147 carbonyl complexes of molybdenum have been determined138 in order to elucidate effects of chelate and carbonyl ligands. Despite the greater steric requirement of the phosphine ligand in the water-soluble [Na-kryptofix-22I],[W(CO),(PR3)] (R = C,H,SO,-rn) compared with PPh, there is close ~irnilarity'~~ with the related PPh complex.On further reaction interligand interactions via the Na+ ion are considered to facilitate the exclusive formation of the cis isomer of [W(CO),(PR,),]6-. Oxidation of (35) gavel4' the compound (36) containing triply-bridging PO ligands. An unusual form of phosphinidene bridging has been obtainedl4* in (37)with a double and a single bond to tungsten atoms of different oxidation numbers. While the cyclopentadienyl complex is thermally very stable the pentamethylcyclopentadienyl homologue readily eliminates PH,mes to give the more common form of the cyclic symmetrical phosphinidene complex (38).(E,E)-3,4-bis(2,4,6-Tributylphenylphos-phinidene)-(1,2-trimethylsilyl)cyclobutene (39) reacted'42 with Group 6 hexacar- bonyls or [M(CO),(thf)] or [M(CO),(nbd)] to give the stable complexes [M(CO),L]. There is a linear relationship between 31P NMR chemical shifts and the mass of the metal atom. (35) Mes I (L= Cp') * L (37) L = cp cp* 2,2'-bis(3,4-DimethyIphosphinine)reacted', with [Cr(CO),(thf)] to give the symmetrical complex (40).The P-CI bond is longer than the P-C-6 bond within each phosphinine ring in contrast to both of the analogous bipy and 2-phosphinine- 2'-pyridine complexes where the corresponding bonds are closely similar in length. Titration calorimetry has been to determine the heats of protonation of cis-[M(CO),(L-L),] (M = Cr Mo W; L-L = dppm dppe dppp arphos dmpe) 13R C.-H.Ueng and G.-Y. Hwang Acra Crystallogr. Sect. C. 1991,47 522; C.-H. Ueng and L.-C. Leu Acra Crystallogr. Ser. C 1991 47 725. 13Y D. J. Darensbourg C. J. Bischoff. and J. H. Reibenspies Inorg. Chem. 1991. 30 1144. 140 0.J. Scherer J. Braun P. Walther G. Heckmann and G. Wolmershaeuser. Angel?. Chem. 1991,103.861. 141 W. Malisch U.-A. Hirth T.A. Bright H. Kab T. S. Ertal S. Huckmann and H. Bertagnolli. Angrw. Chem. Int. Ed. Engl. 1992 31 1525. 142 K. Toyota K. Tashiro. and M. Yoshifuji Chem. Lett. 1991. 2079. 143 P. Le Floch D. Carmichael L. Ricard and F. Mathey J. Am. Chem. SOL..,1991 113 667. 144 J. R.Sowa Jr. J. 9. Bonanno V. Zanotti.and R. J. Angelici Inorg. Chem. 1992 31. 1370. 148 H. Sloan Ar I SiMe3 %Me3 I Ar oc co (39) Ar = 2,4,6-ti-ibutylphenyl (40) with CF,SO,H in 1,2-dichloroethane. Spectroscopic studies showed protonation at the metal and the heat of protonation becomes less exothermic implying greater basicity as the chelate ring size increases. Replacing phenyl by methyl substituents increases basicity as the ligand becomes a better o-donor. The arsenic complex has a greater heat of protonation in line with the weaker bonding. The effect of changing the metal is to increase basicity and heat of protonation in the order Cr << Mo < W for the dppm series but there is some reversal (Mo > W) for the dppe complexes. An investigation by 'H NMR spectroscopy in CDCI or CD,Cl of the reactions of mer-[MoCl,(thf),] with phosphines has shown145 a clear trans effect in that the thf trans to a chloro ligand is replaced more rapidly than thf opposite to thf.Final products are the trichlorotrisphosphines except for bulkier phosphines which give dinuclear complexes. The most nucleophilic phosphines react with solvent to give additional chloro ligands in tetrachloro complexes. The 95M~ NMR shifts serve146 as a sensitive probe of the nature of PR ligands for a wide range of R types. Correlation with the Kabachnik electronic parameter allows differentiation of (T and zeffects though steric effects may interfere. For chlorophosphines results suggested poor n-acceptor properties in contrast to the view based on IR carbonyl frequencies.While the relative strength of alkylphosphite ligands as z-acceptors is well established that of alkylphos- phines remains poorly understood. The '0 NMR-derived quadrupole coupling constants have been determined147 in a comparative study of the axial and equatorial carbonyl ligands in [W(C0)5{P(OMe),)] [W(CO),(PMe,)] and [W(CO),(NMe,)] and the results provide a quantitative comparison of the n-acceptor properties of the trimethylphosphine ligand. 15 Arsenic-donor Ligands The seven-coordinate complex [WBr,(CO),(PMe,)(dtmah)] has notably shorten- ed148 W-As bonds possibly due to d,-d back donation from tungsten. The differences between these two bonds are ascribed to trans effects in the distorted monocapped trigonal prismatic structure.Chemically imposed disorder occurs149 in the crystal structure offac,fac-[Mo2(C0),(ape),l. One ape ligand bridges the two molybdenum atoms and the facial arrangement of the (CO) moieties leads to the disorder so that it is not possible to distinguish As and P atoms. 145 R. Poli and J.C. Gordon Itiorg. Chem. 1991. 30 4550. 14' E.C. Alyea and S. Song Inorg. Chrm.. 1992 31. 4909. 147 S. P. Wang M. G. Richmond and M. Schwartz J. Am. Chem. Soc.. 1992. 114 7595. i4x S. K. Manocha L. M. Mihichuk R. J. Barton. and B. E. Robertson Acrci Crystcdlogr. Sect. C. 1991 47 722. 149 6. F. Abrahams. R. Colton 6.F. Hoskins and K. McGregor. Ausr. J. Chrm. 1992. 45 941. Cr Mo atid W 149 16 Oxygen-donor Ligands The hexaaquachromium(r1r) cation in [Cr(H2O),]NO,.3H,O is distorted' 50 from octahedral geometry with Cr-0 distances varying from 1.46 to 1.72 A; the 0-Cr-0 angles are all close to but significantly vary from 90".The ESR spectrum of hexaaquomolybdenum(m) has been reinvestigated,' ' with significant differences from a previous report. A neutron diffraction study of the fully deuterated Tutton salt [ND4],[Cr(SO,),]-6D,O shows' 52 a large Jahn-Teller distortion of the cation [Cr(D,O),]". A contribution to the debate over the splitting in the sharp line transitions due to the anisotropic nature of the n-donor interaction of the hydroxyl ligand in [Cr(NH,)5(OH)]2' has been made' 53 with studies of the deuterated and undeuterated complex. Some re-assignment of bands is suggested.Neutron diffraction has provided' 54 improved definition of the disorder of both aquo and cyano ligands in [Co(NH,),(H,O)][Cr(CN),] with both ions of strongly regular octahedral form. The gas phase electron diffraction of chromyl nitrate [CrO,(NO,),] indicated' 55 a severely distorted octahedral structure in that the nitrate groups act as chelating ligands with one short and one long Cr-0 bond (estimated bond order of0.19-0.29 for the long bond). The 0x0 ligands are mutually cis. Outer sphere coordination of organic solvents to [Cr(acac),] and to [Cr(trop),] shows similar effects' 56 in their 'H and '3C NMR spectra suggesting interaction with the inner coordination environment of the metal and oxygen atoms. The structure of trans-[(Cr(en),(ONO)}2(H302)][C104]3 has' 57 two unusual features.As well as the 0-bound nitrito group with the other oxygen directed away from the chromium atom the two metal centres are bridged by an (OH)-H-(OH) chain with the middle H on a centre of inversion for the cation. Photochemical reaction of [W(CO),(thf)] with [NEt,][catH] gavel5* [NEt,],[W(CO),(cat)]-catH for which diffraction studies show continuous hydrogen bonding between bridging catechol and adjacent anions. Hydrogen bonding is present also in solution in MeCN deduced from the higher frequency CO vibrations in the IR and the downfield shift of the I3C NMR peaks. In the complex without the 'solvating' catH, the carbonyl ligands are fluxional and the NMR peaks coalesce at 23°C. The coalescence temperature is reduced by electron-releasing But groups on the cat ligand.Loss of CO occurs in the equilibrium of Scheme 4. The reaction of [CrCl,(thf),] with NaOPr' initially gave' 59 the polymer [{Cr(OPri)2]n] followed by further reaction as in Scheme 5; the final product has to have an octahedral arrangement of Cr,Na with the two chromium atoms in trans 15') D. Lazar B. Ribar V. Divjakovic. and C. Meszaros Actu Crystrullogr.. Sect. C 1991. 47 1060. 15' C.J. H. Jacobsen and E. Pedersen Inorg. Chem. 1991 30 4477. Is.? B . N . F'iggis E. S. Kucharski and J. B. Forsyth. Acta Crystallogr.. Sect. C. 1991 47 419. 153 K.-W. Lee and P. E. Hoggard Inorg. Chm. 1991 30 264. IS4 B. N. Figgis E. S. Kucharski and M. Vrtis Actu Crystullogr. Sect. B. 1991 47. 858. 15' C.J.Marsden K. Hedberg M. M. Ludwig and G. L. Card. Inorg. Chem. 1991 30 4761. 15' A. N. Kitaigorodski and U. Edlund. Actu Chern. Scund.. 1991 45. 534. A.G. McKenna W.T. Pennington and J.C. Fanning Inorg. Chim. Acta 1991 183 127. lSxD. J. Darensbourg K. K. Klausmeyer. B. L. Mueller and J. H. Reibenspies Angew. Chem. Int. Ed. EngI. 1992 31 1503. Is' J.J. H. Edema. S. Garnbarotta W.J.J. Snieets. and A. L. Spek. Inorg. Chem. 1991. 30 1380. 150 H. Sloan R = H Bu' Scheme 4 Scheme 5 positions and a propoxide capping each CrNa face. One thf molecule is ligated to each sodium atom. The influence of ligand and alkali metal counter-ions on the molecular complexity of chromium(I1) aryloxides has been examined.' 6o The products of the reaction of WCl with o-phenylenediamine are affected161 by the nature of the solvent; isopropanol gave binuclear [{ WCl,(Hpda)},(q-pda)] (41) whereas methanol led to the unsymmetric methoxide [W,Cl,(OMe),(p-OMe)2].Complex (41) has different bond lengths for the W-amino (2.2981) and W-amido (1.92 81) bonds in the chelated Hpda; the bridging pda is symmetric with W=N double bonds (1.75 A). The reaction in thf of WOCl, o-phenylenediamine and LiNMe (prepared in situ from Me,NH and commercial BuLi in hexanes) gave the anion [W2Cl,0(ONMe,),] -which has bridging 0x0 and one bridging hydroxylaminato groups both of which are symmetric. X-Ray diffraction studies showed162 that [(W(N-ptol)(OR),},] (R = Me Pr') have alkoxide bridged structures. The bridges are asymmetric (W-0 = 2.072 2.181 A) with the longer bond trans to the terminal arylimido ligands.Proton NMR shows the arylimido ligands to be dynamic in solution though less so than the 0x0 analogues. Anti-ferromagnetic [Cr,(a~ac),(p-0C,H,R)~] (R = H Me C1 OMe NO,) showed163 a magnetic interaction increasing with the pK of the phenate ligands but no significant differences in the UV/visible spectra. X-Ray diffraction studies (R = H Me) indicated a racemic mixture rather than the more common meso form. Thiophenate analogues are also reported. Straight W-O-Cphenoxy bond dispositions were found16' in [WCl,_,(OAr),] (n = I 2; Ar = 2,6-dimethylphenyl) though such bonds are known with angles as small as 117". The complex [Mo,O,(HCO,),]~- with one bridging formato and two bridging 0x0 groups is a useful source165 of aquo-molybdenum ions without the common problem of chloride contamination.The general rule of lengthening of bonds trans to a I60 J. J. H. Edema A. Meetsma. S.Gambarotta S. I. Khan W. J. J. Smeets and A. L. Spek Inorg. Chem.. 1991 30 3639. 16' C. Redshaw G. Wilkinson B. Hussain-Bates and M. B. Hursthouse. J. Chem. Soc.,Dmlton Trans. 1992 555. 162 W. Clegg R. J. Errington and C. Redshaw J. Chem. Soc. Dulton Truns.. 1992. 3189. 163 M. Nakahanada T. Fujihara A. Fuyuhiro and S. KaiLaki Inorg. Chem. 1992. 31 1315. 164 N. Kanehisa Y. Kai. N. Kasai H. Yasuda Y. Nakayama and A. Nakamura Bull. Chrm. Soc. Jpn. 1992 65 1197. M. Brorson and A. Hazell Actu Chem. Scund. 1991 45 758. Cr Mo and W terminal 0x0 ligand in binuclear molybdenum(v) complexes with two bridging oxygen atoms was confirmed but no such effect was found'66 from structural determinations where the bridging atoms are sulfur.The 18,W NMR chemical shifts of a number of 0x0- sulfido- and nitrido-tungsten(v1) complexes have been measured' 67 by indirect methods. The tungsten nuclei become more de-shielded with increasing ligand polarizibility and bond multiplicity. Ligand substitution of rac-1,l'-binaphth-2-01 (H,bino) with [W,(OBu\),] gave'68 mainly anti-(R,S) compound (42) whereas (R)-H,bino gave the gauche-(S,S) form. The distribution of the various products suggested a high stereospecificity in the reaction. But BU' An unusual oxidation which may involve nucleophilic (pyridine-N-oxide) or electrophilic (HOCl or C1,O) sources of oxygen occurred' 69 when [WCl,(NPR,)] (R =Me Ph) was converted to [WCl,(NCI)(OPR,)].The binuclear Mov complex (43) may be formed17' in several ways (Scheme 6) uia the mononuclear (44). The 0x0 group in (43) comes from the methoxy group in (44). [W(CO),(solvent)] reacted17' readily with oxalate dianion in 1 :1 ratio to form a simple chelated octahedral complex [W(CO),(C,O,)]' -. Reaction with a further equivalent of [W(CO),(solvent)] gave the stable binuclear [W,(CO),(C,O,)]'- in which the oxalate ligand bridges the two tungsten centres simultaneously chelating each tungsten. The latter dinuclear anion can be formed via the intermediate [W2(C0),,(C20,)]' with subsequent loss of CO. ~ The [Mo0,{0,CC(S)Ph,),]2 -anion where the phenyl groups provide sufficient steric hindrance to prevent dimerization reacted'72 with thiols at acid pH to give mononuclear [MoO(O,CC(S)Ph,},] - which has an almost square pyramidal structure and an ESR spectrum typical of oxomolybdenum(v) complexes.Trinuclear compounds with a triangle of three metal atoms around a central oxygen atom are well known in this and other transition metal groups. The complex [Cr,(p3-O)(p-0,0'-L-valine)6(H20),]7+has' 73 a planar trigonal disposition of 1hh B. Karnenar B. Kaitner and N. Strukan. Craut. Chem. Actu. 1991 64. 329. 167 Y. Ma P. Demou and J. W. Faller Inory. Chem. 1991 30 62. 168 S.D. Dietz. N. W. Eilerts and J. A. Heppert .4nyetv. Chem. Int. Ed. Engl. 1992. 31. 66. 169 J.D. Lichtenhan J. W. Ziller and N. M. Doherty Inorg. Chem.. 1992 31 4210. I 70 M. Minelli R. L. Kuhlrnan S.J. Shaffer and M. Y. Chiang Inorg. Chem. 1992 31 3891. 171 D.J. Darensbourg J.A. Chojnacki and J. H. Reibenspies Inory. Chrm. 1992 31. 3428. 172 V. Sanz T. Picher P. Palanca P. Gomez-Romero E. Llopis. J. A. Ramirez D. Beltran and A. Cervilla. Inorg. Chem. 1991 30. 3113. I73 H. Kato. K. Nakata A. Nagasawa T. Yamaguchi Y. Sasaki and T. Ito Bull. Chem. SOC.Jpn. 1991,64. 3463. 152 H. Sloan 0 FF t B; Br t N. / OMe (44) 0 Z = o-HS.C,H,.NH2 in MeOH + 2NF13. S-S = Et,NCS; Scheme 6 chromium atoms about a central oxygen atom. The electronic spectra and magnetic moments show that this and other analogous amino acid complexes are weakly anti-ferromagnetic.Compounds with two such edge-sharing triangles in an M40z core are now being explored. Dissolution of [Cr(H,O),](OAc) or [Cr,O(OAc),(H,O),]Cl in molten bipy at 80 ^C followed by addition of water and KPF, gave” [Cr,O,(OAc),(bipy ),][PF,]. The central Cr,O core of this compound is bent in the ‘butterfly’ mode previously found in analogous Mn and Fe carboxylates. Three acetato ligands bridge the terminal to central chromium atoms while the seventh acetato ligand bridges the two central chromium atoms. The adamantane-like Mo,P,O cage is retained’” unchanged during the reaction of (45) with halogens as in Scheme 7. Bromination contrasts with other halogenations in that a dibromo intermediate is not obtained in the direct reaction with (45).X-Ray diffraction studies of (46 X = I) show a trigonal prismatic structure around each 16-electron molybdenum(r1); NMR spectroscopy shows retention of this configuration by (46) and (47) in non-polar solvents. At low temperatures intermediate (48) was observed. When the NPr’ substituent is replaced by Ph similar reaction conditions give products (49) and (50) which are of low stability and lose CO readily. ”‘A. Bino. R. Chayat. E. Pedersen. and A. Schneider. Inorq. Cheni.. 1991. 30. X56. 1’5 M. M. Turnbull. C. Valdez. E. H. Wonp. E. J. Gabe. and F. L. Lee Itrory. Chmi. 1992. 31. 208. Cr Mo and W X = 1 R = NMeZ X2(C0)2Mo[RPO]4M~(C0)2X2 (46) X = Br low temp. or X = CI Br. I; R = Ph (47) I (48) X = I R = NMe2 (50) X = (31 Br I (49) X = C1 Br I R = Ph Scheme 7 17 Sulfur-donor Ligands and Sulfides Simple ligand substitution of [MoO,(acac),] gives' 76 cis-[Mo02(2-pymS),] (51) and cis-[Mo02(2-pyS),].These Mo"' complexes are quantitatively converted to the binuclear MoV compounds [Mo20,(2-pymS),] and [Mo20,(2-pyS),] by oxygen abstraction with PPh,. Compound (51) is distorted octahedral with cis-0x0 and trans-thio groups having different Mo-S distances. The crystal structures of a number of sterically hindered molybdenum-pyridine-2-thiol complexes show' 77 various coordination modes including unidentate-S chelate-(N,S) or bridging-S. In [NEt,][MoO(~,2-toluenedithiolato)~] the MOOS core is a distorted tetragonal pyramid178 with trans-chelating ligands.Dithiocarbonates reacted' 79 with tet-rathiometalates to give 1,2-dithiolene complexes (Scheme 8). Electrochemical studies show that these undergo two one-electron oxidations at mild potentials. [Mo(S,C,S,CO),] was prepared by oxidation of the corresponding dianion with nitrosonium or ferrocenium salts. Aqueous [Mo0,12 -and polysulfide reacted' 8o on heating to form the dinuclear anion (52a). Tungstate required preliminary reduction before undergoing a similar reaction to give (52b) and (53). The disodium dithiolate Na,(mnt) reacted' 81 with [Mo,(O,CMe),] to replace completely the acetate ligands and reduce the multiplicity of the quadruple Mo-Mo bond giving (54). The molybdenum atoms of this complex are within a distorted square pyramid with terminal 0or Sat the apex and in a syn conformation.The similar complex [Mo2(p-O),O2C1,(dmbip~),](55)was prepared by reaction of dmbipy and I76 P. R. Traill. A.G. Wedd and E. R.T. Tiekink ..lust. J. Chrm. 1992 45. 1933. 177 E. Block M. Gernon. H. Kang G. Ofori-Okai and J. Zubieta Inorg. Chern. 1991 30 1736. 178 N Ueyama N. Yoshinaga. A. Kajiwara A. Nakamura. and M. Kusunoki Bull. Chrm.Soc. Jpn.. 1991.64. 2458. I79 X. Yang. G. K. W. Freeman T. 9. Rauchfuss and S. R. Wilson Inorg. Chem.. 1991 30. 3034. I80 R. Bhattacharyya P. K. Chakrabarty P.N. Ghosh. A. K. Mukherjee D. Podder and M. Mukherjee. Inorg. Chem. 1991 30. 3948. in1 J. I. Dulebohn T.C. Stamatakos D. L. Ward and D.G. Nocera. Polyhedron. 1991 10. 2813. 154 H.Sloan Scheme 8 [Mo,Cl,(NCMe),] or by oxidation with dioxygen of [Mo,Cl,(dmbipy),]. The metal-metal distances of 2.858 8 (in 54) and 2.562 A (in 55) are typical of MoV-MoV single bonds. (52) a M= Mo; (53) b M=W I \ NC CN The orthorhombic form of [Cr"'(SSPMe,),] crystallized from ethanol has' 82 the same trigonal prismatic structure found in the monoclinic form obtained by sublimation. Disodium 4,5-dimercapto-1 ,3-dithiole-2-thionate7 Na,C,S, reacted' 83 with MoCl to give the distorted trigonal prismatic complex [NBu,][Mo(C,S,),]. The ligand 4-(4-hydroxyphenyl)pyridine has been used' 84 to bridge the 16-electron 0-coordinated molybdenum centre and the 17-electron N-coordinated molybdenum centre of [(MoCl(NO)Tp'}(OC,H,C,H,N)(MoCl(NO)Tp')].There is considerable interaction between the two molybdenum centres across the bridging ligand as shown by electrochemistry and ESR spectroscopy. Labile dinuclear Mo"' complexes are formed'85 by sulfur extraction from SPMe as in Scheme 9. Crystal structural analyses for all three compounds (56) (57) and (58) were made and the coordinatively unsaturated nature of (57) confirmed. E. Skrzypczak-Jankun and A.A. Pinkerton Acra Crystallogr. Sect. C 1991 47 2211. le3 G. Matsubayashi K. Douki and H. Tamura Chem. Leu. 1992 1251. 184 A. Das J. C. Jeffery J. P. Maher J. A. McCleverty E. Schatz M. D. Ward and G. Wollermann Angew. Chem. Int. Ed. Engl. 1992. 31. 1515. '" K.A. Hall S.C. Critchlow and J. M. Mayer. Inorg. Chrm. 1991 30. 3593. Cr Mo and W c1 PMe c1 I I Me3P Mo PMe3 + SPMe3 -80" MO-/CI,M6PMe, Me3P' I PMe3 Me3P'I \s'I PMe3 c1 PMe C1 (56) +PMe3 -PMq 11 PMe3 C1 PMe C1 +MeCN MO-Mo-PMe3 N PMe3 PMe C1 C Me (57) (58) Scheme 9 The reaction of [Mo,S,Br,] with PBu in thf gave'86 the anion [Br,OMo(p- S),MoOBr,12-which has a bent MS,M bridge with terminal syn M=O groups; an unusual reaction of thf to give [Bu,P(CH,),PBu,12 +,provides the counter-ion.The reaction of [M20,S2I2- (M = Mo W) with sulfur and hydrazine hydrochloride gave'87 complexes [(MO(S2)2}2(S,)(p2-NH2NH2)]2with long polysulfide chains -forming one of the bridging ligands. The other bridge has a zig-zag M-N-N-M chain where hydrazine bridges the two metal centres in an end-on mode.Each half of the molybdenum-containing anion is pentagonal bipyramidal with the five sulfur atoms in the equatorial plane. There is some statistical disorder in the S chain. The in situ reaction of CS and PR (R = Et Bu Cy) with (59) gave'" complexes (60)which have q3-S,C,S' coordination to Mo and q2-S,S' coordination to Sn. There is no direct molybdenum-tin bond but a weak Sn-C1 bond provides further bridging between the metal atoms. Treatment of a suspension of [W(CO),] in refluxing CH,Cl with S,Cl,. while irradiating with tungsten light gave'89 the adduct WCl,S.S where the WC1,S unit F.A. Cotton R. L. Luck and C.S. Miertschin Inorg. Chem. 1991 30 1155. I*' N. Zhu S. Du X. Wu and J. Lu. Angew'.Chem. Int. Ed. Engl. 1992,31. 87; S. Du N. Zhu X. Wu and J.Lu Inorg. Chem. 1992 31 2847. IH8 D. Miguel J. A. Perez-Martinez V. Riera. and S. Garcia-Granda. Anyew. Chrm. Inr. Ed. Enyl.. 1992.31. 76. D. L. Hughes J. D. Lane and R. L. Richards. J. Chcm. Soc. Dulron Truns..1991. 1627. 156 H. Sloan forms a square pyramid with apical S. The S ring occupies a position below the base of the pyramid with the distances of the chlorine atoms to three of the sulfur atoms of the S ring being significantly shorter than the van der Waals distances. The shortest W-SFi, distance is close to the sum of the van der Waals radii. 18 Selenium- and Tellurium-donor Ligands Gas-phase electron diffraction of WSBr and WSeBr has shown'" a regular square pyramidal structure with the chalcogen at the apex and the tungsten atom above the plane of the bromine atoms.A mass spectral study of [Mo3(p3-X)(YZ),(dtc),] (X Y Z = S;X Y = S Z = Se; X = S Y Z = Se) showed'" similar fragmentation patterns with easier loss of chalcogen in the equatorial position compared with the bridging X atom. Coordinatively unsaturated metal centres occur in the symmetric [W,Se2(PPh2Me),(SePh),].2thf which was prepared" by the reaction of SiMe,(SePh) with [WCl,(PPh,Me),] in thf at room temperature. The centro- symmetric complex has asymmetric W-Se-W bridges (2.380 2.473 A) a distortion which is similar to that found in [W,Se,]'- and [W,Se,,l2-. The coordination sphere of each tungsten is made up by one phosphine and two selenolate ligands to give distorted trigonal-bipyramidal geometry. The [Wv'Se,12 -anion underwent 193 an induced internal electron-transfer in its reaction with R,NC(S)SSC(S)NR (R = Et Bu') to form the eight-coordinate [WVSe,(S,CNR,),].There is a correlation of the lowest energy CT band with the reactivity of [ME,]"- for M/E combinations Mo/S W/S W/Se V,'S. Re/S; [WSe,]'~ has similar reactivity to [MoS,I2-. The isostructural selenides [PPh,],[M,(WSe,),] (M = Pb Sn) contain'94 four tetrahedral WSe moieties but two of these share one edge with an MSe octahedron; the other two share two edges with a Se vertex common to both MSe octahedra (61 ). Oxidative decarbonylation of molybdenum and tungsten hexacarbonyls by the anion [As,Se,]'- gave"' (62) while use of [As2Se,I3- gave (63). The former can be converted to the latter by the addition of red selenium.There is an unusual asymmetric unit cell with three discrete chemically-similar anions in (62b) with mixed As/Se coordination in a trigonal prismatic arrangement around tungsten and the two carbonyl ligands capping two of the square faces. In contrast (63) is six-coordinate through selenium only with some interaction between one selenium atom on each of the two ligands to support bonding. Complex (63 M = Mo) also resulted'96 from the reaction of [PPh,][MoSe,] with excess As,Se although [NBu,][WSe,] with excess As,Se gave the dianion (64). The first terminal transition-metal-tellurium double bond is reported' 97 in tvans-[W(PMe,),(Te),] (65) where the W-Te bond length (2.596A) is shorter than known W-Te single bonds (typically 2.68-2.88 A).Evidence suggests that Me,PTe is a catalytically active species in the formation of 190 E. M. Page. D.A. Rice K. Hagen L. Hedberg and K. Hedberg. Inory. Chern.. 1991 30. 4758. I91 K. Hegetschweiler. P. Caravatti V. P. Fedin a;id M. N. Sokolov. Heir.. Chim. Acro 1992 75 1659. 19* P. M. Boorman. H.-B. Kraatz. and M. Parvcz. J. Chem. Soc.. Dalton Truns. 1992. 3281. Y. Gea. M.A. Greaney. C. L. Coyle and E. I. Stiefel. J. Chem. Soc.. Chern. Comrnun.. 1992. 160. Y.-J. Lu and J.A. Ihers 4crn Cry,\tulloyr.. Sect. C. 1991 47 1600. 19' S.C. O'Neal. W.T. Pennington and J. W. Kolis. Inorq. Chern. 1992. 31. 888. S.C. O'Neal. W.T. Pennington and J. W. Kolis J. Am. Chern. Soc. 19Y I. 113 710. I')' D. Rabinovich and G. Parkin. J. Am. Ckern. Soc. 1991.113. 9421. Cr Mo and W Se\W/Se Se-M-I Se-W-Se \ Se-M-/\ se\ /Se /\ Se \ L (62) a M = Mo b,M=W \/““-rSe Se 2-/e-Se,-,Se -As\\se7MyseAjAs Se/w\se Se-Se Se-Se (61) M=Pb,Sn (63) M =Mo W r Se /Se-Se I 12- (65)from [WH(PMe3),(q2-CH2PMez)] and elemental tellurium. A similar reaction of (65) with HIS gave the sulfur analogue by elimination of hydrogen. The central M,Te rhomboid cores in [M,(CO),,(p,-Te)z] (M = Cr W) have 198 long metal-metal distances though distortion from tetrahedral form around Te for both compounds and magnetic data for the tungsten compound support the presence of a metal-metal bond. ~ In [Cr,(CO)20(q2,p,-Te,)]2 and in [Cr,(CO)zo(t~2.p3-Te3)]2four Cr(CO) -fragments are attached to the end tellurium atoms of the two and three atom chains respectively with no other bridging to the Cr atoms; there is disorder of the middle tellurium atom in the bent Te chain of the latter anion.19 Halide Ligands The structure of [CrF,] has attracted attention with theoretical studies pre- dicting trigonal prismatic’99 and octahedral”’ structures. Experimental data are 14” L.C. Roof. W.T. Pennington. and J.W. Kolis. Inorq. Chcw. 1992. 31. 2056. I” C.J. Marsden and P. P. Wolynec. Inorg. Chem.. 1991. 30 1681. K. Pierloot and B.O. Roos. Inorg. C/~WI..1992. 31. 5353; A. Neuhaus. G. Frenking C. Huber and J. Gauss. Inorq. Ch~m.,1992. 31. 5355. 158 H. Sloan held201 to indicate an octahedral structure though some analysis suggested'" that its existence is doubtful.In the [WSF,] -anion the tungsten atom is displacedzo3 above the plane of the equatorial fluorine atoms of the octahedral structure towards the sulfide ligand. There is disorder between the sulfide and axial fluoride ligands in the crystal. NMR spectroscopy shows no exchange between the axial and equatorial fluoride ligands in solution. A reversible colour change dependent upon pH was found'' with (66) where hydroxide addition occurs on the fluorinated acac ligand. The equilibrium constant is four orders of magnitude larger than for the corresponding hydroxylation of the cobalt analogue. ,CFJ 2+ Triple fluoro bridges were foundzo5 in binuclear [{ W(CO)2(PMe2Ph)2}2(pF)3] [BF,] prepared from [WH,(PMe,Ph),] and HBF,.OEt,.The crystal structure shows each tungsten atom between parallel planes of the fluorine atoms and of the other ligands. In the latter plane the carbonyl and phosphine ligand pairs are in trans dispositions. Near-IR emission and absorption spectral studies of the strongly exchange-coupled dinuclear anion of Cs,[Mo,Cl,] showed"' significant weakening of the Mo-Mo bond in the excited state corresponding to a lengthening of about 0.1 A. The chloro bridges in [Mo(~-C~),O,C~,]~ -arezo7 asymmetric. The anion of [htmmp][W,CI,] has208 a W-W distance of 2.409 A emphasizing the tendency for third row elements to give more rigid metal-metal bonds; the related [Mo,CI,]~ compounds show greater variability of the metal-metal bond length. Reaction of [Mo,(OAc),] with SiCIMe and dppe in thfkoluene followed by layering the pink solid in a solution of CH,Cl,/py with hexane gave2'' [Mo,Cl,(OAc),(py),] as one of the products.The acetate ligands bridge the Mo-Mo bond in a cis configuration and the molecules are linked into infinite chains by asymmetric chloride bridges (Mo-Cl = 2.440 3.082 A). From this and similar compounds the trans effect on the Mo-O,,,,,, bond is in the order PEt > Bu'CO 3 C1 > py. The Mo-I bond in [MoOI(dmpe),] + was found' lo to be very long at 2.964 A most likely because of the trans influence of the 0x0 ligand. ''I E.G. Hope W. Levason. and J. S. Ogden Inory. Chem. 1991 30,4873. 202 J. Jacobs H.S. P. Muller H. Willner. E. Jacob. and H. Burger Inory. Chem.. 1992 31. 5357. 2n3 M.Hilbers M. Liige and R. Mattes Inory. Chim. Acfn 1992 201 I. 2"4 T. Katou Y. Yamamoto K. Kuroda. K. Watanabe and Y. Kitamura Inory. Chim. Acta. 1991 180,13. 205 D. M. Dawson R.A. Henderson A. Hills and D.L. Hughes J. Chem. Soc.. Dalton 7i.ans.. 1992 973. 'Oh R. Stranger. G. Moran E. Kransz. L. Dubicki H. Gudel and N. Furer Inory. Chem.. 1992 31. 2860. 207 R. Herbst-Irmer and E. Egert Actu Crystallogr..Sect. C. 1992. 48 1843. 208 K.R. Dunbar and L. E. Pence. Acta Crpstalloyr.. Sect. C. 1991. 47. 23. 2"y J.-D. Chen. F.A. Cotton and S.-J. Kang. Inorg. Chim. Acta. 1991. 190. 103. 'In B. E. Owens and R. Poli. Ac~aCrystallogr.. Sect. c'. 1992. 48. 2137.