Nicholas Carr

Platinum ethyl complexes with β-agostic Pt–H–C bonding

Protonation with non-co-ordinating acids of the complexes [Pt(η2-C2H4)(L–L)][L–L =(H11C6)2P(CH2)2P(C6H11)2, 1a, But2P(CH2)2PBut2, 1b, (H11C6)2P(CH2)3P(C6H11)2, 1c, But2P(CH2)3PBut2, 1d or o-But2PCH2C6H4CH2PBut2, 1e] and [PtEt2(L–L)]2a–2d affords a series of cationic platinum(II) complexes 3a–3e which in the case of 3a–3c adopt a cis ethene/hydride ground state whereas in 3d and 3e the otherwise electron-deficient metal centre is stabilized by a two-electron, three-centre agostic interaction with the β-CH bond of the ethyl ligand. Complexes 1–3 were characterized by 1H, 13C and 31P NMR spectroscopy and for 2d and 3d by single-crystal X-ray crystallography. The influence of the chelating diphosphine ligand on the strength of the agostic bond was monitored by NMR spectroscopy. This revealed that the cations undergo two fluxional processes in solution: (a) agostic methyl rotation and (b)β-elimination/ethene rotation, a combination of which scrambles all five protons and both carbon atoms of the ‘C2H5’ moiety. The 31P nuclei, however, remain inequivalent at temperatures up to 300 K. The agostic interaction was displaced by a small two-electon donor molecule L to form the series of adducts [PtEt(L)(L–L)]+(L = acetonitrile or pyridine) in which the ‘normal’ ethyl complex is the first formed species. The adducts are unstable to loss of C2H4 by β-elimination to form the series of cationic hydrides [PtH(L)(L–L)]+. For comparison, the complex [PtH(O3SCF3){But2P(CH2)3PBut2}] was synthesised and characterized by 1H and 31P NMR spectroscopy and X-ray crystallography.

Ligand control of agostic M ⋯ H ⋯ C three-centre, two-electron bonding in bicyclo[2.2.1]hept-2-yl complexes of platinum and palladium. X-Ray crystal structures of [Pt(η2-C7H10){But2P(CH2)2PBut2}] and [Pt(C7H11){But2P(CH2)2PBut2}][BPh4]

The reaction of non-co-ordinating acids with the Pt0 and Pd0 alkene complexes [M(η2-C7H10)(L–L)][M = Pt or Pd; L–L =(C6H11)2P(CH2)2P(C6H11)2, 1a or 1f: But2P(CH2)2PBut2, 1b or 1g; and o-C6H4(CH2PBut2)2, 1e or 1h; M = Pt, L–L =(C6H11)2P(CH2)3P(C6H11)21c or But2P(CH2)3PBut21d] affords a series of cationic bicyclo[2.2.1]hept-2-yl complexes 2a–2h in which the otherwise electron-deficient metal centre is stablized by a three-centre, two-electron (agostic) interaction with the exo-3-CH bond. The complexes were characterized by 1H, 13C and 31P NMR spectroscopy and for 1b and 2b by single-crystal X-ray crystallography. In complex 1b the norborn-2-ene is bound to the platinum in a normal in-plane η2-mode with equal Pt–C distances [2.110(7), 2.108(8)A] and Pt–P distances [2.273(2), 2.274(2)A]. For 2b the crystallographic results reveal a long Pt–Cβ contact of 2.309(5)A which is bridged by a hydrogen atom forming the agostic bond, whereas the Pt–Cα bond is shortened to 2.096(4)A. The Pt–P bond trans to the weak agostic bond is significantly shorter than the cis Pt–P bond [2.256(1) and 2.311(1)A respectively], and this asymmetry in the co-ordination of the diphosphine is reflected in the 31P NMR spectrum of 2b for which 1J(PtPtrans)1J(PtPcis). The extent of agostic interaction, as indicated by NMR parameters [1J(PtH), 1J(PtPtrans), etc.], depends on the bite angle of the diphosphine and the bulk of the substituents on phosphorus such that the smallest diphosphines induce the strongest M ⋯ H ⋯ C interaction. All the agostic complexes undergo a rapid intramolecular rearrangement on the NMR time-scale at room temperature involving β-elimination and alkene rotation. However, the 31P nuclei remain non-equivalent up to 300 K.

Chemistry of polynuclear metal complexes with bridging carbene or carbyne ligands. Part 106. Synthesis and reactions of the alkylidyne complexes [M(CR)(CO)2{(C6F5)AuC(pz)3}](M = WorMo, R = alkyloraryl, pz = pyrazol-1-yl); crystal structure of [WPtAU(C6F5)(µ3-CMe)(CO)2(PMe2Ph)2{(C6F5)AuC(pz)3}]

Treatment of the salts [M (CR)(CO)2{HC(pz)3}][BF4][M = W or Mo, R = alkyl or aryl, HC(pz)3= tris(pyrazol-1 -yl)methane] in thf (tetrahydrofuran) with NaOEt, followed by [Au(C6F5)(tht)](tht = tetrahydrothiophene), affords the neutral alkylidynemetal compounds [M(CR)(CO)2{(C6F5)AuC(pz)3}](M = W or Mo, R = C6H4Me-4; M = W, R = Me or C6H3Me2-2,6). The complexes (M = W, R = Me or C6H4Me-4) have been used to prepare several compounds containing heteronuclear metal–metal bonds, including [WAuX(µ-CMe)(CO)2{(C6F5)AuC(pz)3}](X = Cl or C6F5), [WCo2(µ3-CR)(CO)8{(C6F5)AuC(pz)3}], [WPt(µ-CR)(CO)2(PMe2Ph)2{(C6F5)AuC(pz)3}], and [W2Pt(µ-CR)2(CO)4{(C6F5)AuC(pz)3}2]. The cluster compound [WPtAu(C6F5)(µ3-CMe)(CO)2(PMe2Ph)2{(C6F5)AuC(pz)3}] has been synthesised by different routes, and its structure established by X-ray diffraction. The core of the molecule consists of a WPtAu triangle [W–Pt 2.798(2), W–Au 2.841(2), and Pt–Au 2.932(2)A] asymmetrically capped by an ethylidyne group [µ-C–W 2.06(3), µ-C–Pt 2.05(3), and µ-C–Au 2.31 (3)A]. The latter lies appreciably further from the Au atom than from the W or Pt atoms. The two carbonyl ligands semi-bridge the W–Pt [W–C–O 160(2)°] and W–Au [W–C–O 165(3)°] bonds. The Pt atom carries the PMe2Ph groups [P–Pt 2.26(1) and 2.32(1)A], and the Au atom is co-ordinated by the C6F5 group [C–Au 2.04(3)A]. The W atom is ligated by the three nitrogens of the (C6F5)AuC(pz)3 moiety (N–W average 2.21 A). The n.m.r. data (1H, 13C-{1H}, 31P-{1H}, and 19F-{1H}) for the new compounds are reported and discussed where appropriate.

Chemistry of polynuclear metal complexes with bridging carbene or carbyne ligands. Part 100. Synthesis of mixed-metal compounds via the salts [NEt4][Rh(CO)L(η5-C2B9H9R2)](L = PPh3, R = H; L = CO, R = Me); crystal structures of the complexes [WRhAu(µ-CC6H4Me-4)(CO)3(PPh3)(η-C5H5)(η5-C2B9H11)] and [WRh2Au2(µ3-CC6H4Me-4)(CO)6(η-C5H5)(η5-C2B9H9Me2)2]·0.5CH2Cl2

The rhodacarbaborane salts [NEt4][Rh(CO)L(η5-C2B9H9R2)] have been used to prepare the mixed-metal complexes [RhAu(CO)(PPh3)L(η5-C2B9H9R2)](L = PPh3, R = L = CO, R = Me), [WRhAu(µ-CC6H4Me-4)(CO)3L(η-C5H5)(η5-C2B9H9R2)](L = PPh3, R = H; L = CO, R = Me), and [WRh2Au2(µ3-CC6H4Me-4)(CO)6(η-C5H5)(η5-C2B9H9Me2)2]. In relate studies treatment of the salt [WAuCl(µ-CC6H4Me-4)(CO)2(η-C5H5)] with Na[Mn(CO)5] or [N(PPh3)2][Co(CO)4] yields, respectively, the trimetal compounds [WMAu(µ-CC6H4Me-4)(CO)n(η-C5H5)](M = Mn, n= 7; M = Co, n= 6). The molecular structures of [WRhAu(µ-CC6H4Me-4)(CO)3(PPh3)(η-C5H5)(η5-C2B9H11)] and [WRh2Au2(µ3-CC6H4Me-4)(CO)6(η-C5H5)(η5-C2B9H9Me2)2] have been determined by single-crystal X-ray diffraction studies. In the trimetal species there is a bent [156.9(1)°] W–Au–Rh array of metal atoms [W–Au 2.732(1) and Rh–Au 2.640(1)A] with the W–Au bond asymmetrically bridged by the p-tolylmethylidyne group [µ-C–W 1.90(1) and µ-C–Au 2.13(1)A]. The W atom carries the C5H5ring and two CO groups, while the Rh atom is ligated by the η5-C2B9H11 cage, a CO group, and the PPh3 ligand [Rh–P 2.340(3)A]. The pentanuclear metal cluster has a WAu2triangular core [W–Au (average) 2.750(2) and Au ⋯ Au 2.969(2)A] capped by the CC6H4Me-4 group [µ3-C–W 2.02(2) and µ3-C–Au (average) 2.05(2)A]. The tungsten atom is co-ordinated by two CO groups and the C5H5 ring. Each gold atom is linked to a Rh(CO)2(η5-C2B9H9Me2) fragment via both a Rh–Au bond [average 2.217(2)A] and a B–H⇀Au three-centre two-electron bond. This linkage involves for each cage the unique boron atom in the face of the icosahedral C2B9H9Me2fragment which is β to the CMe groups. The spectroscopic properties (i.r., 1H, 13C-{1H}, 31P-{1H}, and 11B n.m.r.) of the new compounds are reported, and where appropriate the data are discussed in relation to their structures.

Synthesis and reactivity of η2(4e)-alkyne and η2(3e)-vinyl complexes of rhenium

Reaction of cis-/trans-[ReBr2(CO)2(η-C5H5)] with PhC2Ph and MeC2Ph in refluxing toluene afforded good yields of the η2(4e)-donor alkyne complexes [ReBr2(η2-PhC2Ph)(η-C5H5)]1 and [ReBr2(η2-MeC2Ph)(η-C5H5)]2, respectively. Treatment of 1 and 2 with either AgBF4 or TlPF6 in the presence of PPh3, PMePh2 or P(OMe)3(L) gave monocations [ReBr{η2(4e)-alkyne}L(η-C5H5)]+, whereas a similar reaction with 2 equivalents of AgBF4 and 1 equivalent of Ph2PCH2CH2PPh2(dppe) afforded dications [Re(η2-PhC2Ph)(dppe)(η-C5H5)][BF4]2 and [Re(η2-MeC2Ph)(dppe)(η-C5H5)][BF4]2. The structural identity of [ReBr(η2-PhC2Ph)(PMePh2)(η-C5H5)][PF6] was confirmed by single-crystal X-ray crystallography. The alkyne C–C vector lies parallel to the Re–Br bond and the alkyne C–C bond length [C(1)–C(2) 1.26(4)A] is relatively short. Treatment of [ReBr(η2-PhC2Ph)(PPh3)(η-C5H5)][BF4] and [ReBr(η2-PhC2Ph)(PMePh2)(η-C5H5)][PF6] with K[BHBus3] in dichloromethane at –78 °C led to neutral η2(3e)-vinyl complexes [[graphic omitted]HPh}Br(PPh3)(η-C5H5)] and [[graphic omitted]HPh}Br(PMePh2)(η-C5H5)]. The crystal structure of the latter showed that the C–C vector of the vinyl moiety lies almost parallel to the Re–Br bond. The stereochemistry of these reactions is discussed in the light of extended-Huckel molecular orbital calculations. Reaction (–78 °C) of [Re(η2-PhC2Ph)(dppe)(η-C5H5)][BF4]2 with 1 equivalent of K[BHBus3] in tetrahydrofuran afforded the X-ray crystallographically identified monocationic η2(3e)-vinyl complex [[graphic omitted]HPh}(dppe)(η-C5H5)][BF4], which reacted at room temperature with a further equivalent of K[BHBus3] to give the cis-stilbene-substituted complex [Re(η2-Z-PhCHCHPh)(dppe)(η-C5H5)]. The crystal structure of the latter showed that the alkene phenyl substituents are orientated towards the cyclopentadienyl ring. In contrast, a similar reaction between K[BHBus3] and [Re(η2-MeC2Ph)(dppe)(η-C5H5)][BF4]2 gave initially the η2(3e)-vinyl complex [[graphic omitted]HPh}(dppe)(η-C5H5)][BF4]; a further equivalent of K[BHBus3] led to deprotonation and formation of the η2-allene complex [Re{η2-CH(Ph)CCH2}(dppe)(η-C5H5)], in which the substituted allenic bond is co-ordinated to the rhenium. The dinuclear complex [Re2Br2(PPh3)2(µ-O)(η-C5H5)2][BF4]2 was also prepared and shown crystallographically to possess a single rhenium–rhenium bond [2.731(5)A].

Chemistry of polynuclear metal complexes with bridging carbene or carbyne ligands. Part 99. Synthesis of the cluster compounds [MWCoAu(µ-CC6H4Me-4)(µ3-CR)(CO)4(η-C5H5)(η-C5Me5)(η5-C2B9H9Me2)](M = Mo or W, R = C6H4Me-4; M = W, R = Me); crystal structure of the complex [MoWCoAu-(µ-CC6H4Me-4)(µ3-CC6H4Me-4)(CO)4(η-C5H5)(η-C5Me5)(η5-C2B9H9Me2)]·CH2Cl2

The trimetal complexes [MWAu(µ-CC6H4Me-4)2(CO)4(η-C5H5)(η5-C2B9H9Me2)](M = Mo or W), with molecular structures based on a MAuW spine and each metal–metal bond bridged by a p-tolylmethylidyne group, react with [Co(η-C2H4)2(η-C5Me5)] in CH2Cl2 at room temperature to afford the tetranuclear metal compounds [MWCoAu(µ-CC6H4Me-4)(µ3CC6H4Me-4)(CO)4(η-C5H5)(η-C5Me5)(η5-C2B9H9Me2)]. An X-ray diffraction study on the molybdenum-containing product revealed a structure with the Co(η-C5Me5) fragment co-ordinated to the 4-MeC6H4C = W(CO)2(η5-C2B9H9Me2) group of the precursor. The cobalt atom is also bonded to the gold, so the metal core consists of a WCoAu triangle [W–Co 2.597(2), W–Au 2.826(1), and Co–Au 2.580(2)A] spiked by the molybdenum [Mo–Au 2.763(2)A]. The p-tolylmethylidyne ligands asymmetrically bridge the metal sites. One group spans the Mo–Au bond [µ-C–Au 2.11(1) and µ-C–Mo 1.90(2)A], and the other the WCoAu triangle [µ-C–Au 2.30(1), µ-C–Co 1.86(1), and µ-C–W 1.97(1)A]. The Mo, W, and Co atoms are co-ordinated by the η-C5H5, η5-C2B9H9Me2, and η-C5Me5 groups, respectively. The Mo and W atoms each carry two CO ligands, but one of these attached to tungsten semi-bridges the W–Co bond [W–C–O 163(1)°]. The reaction between [Co(η-C2H4)2(η-C5Me5)]and[W2Au(µ-CMe)(µ-CC6H4Me-4)(CO)4(η-C5H5)(η5-C2B9H9Me2)] affords a mixture of two isomeric products. Their structures correspond to the alternative possibilities of addition of a Co(η-C5Me5) fragment to either the MeC = W(CO)2(η5-C2B9H9Me2) or the 4-MeC6H4C = W(CO)2(η-C5H5) group in the precursor, but the former isomer predominates. The spectroscopic (i.r. and n.m.r.) properties of the new compounds are reported and discussed.

A tungstendiiron cluster [NEt4][WFe2μ3-η3, η5-CHCC(t Bu)C(O)C2B9H8Me2(CO)8] derived from [Fe2(CO)9] and [NEt4][W CCCtBu)(CO)2-(η5-C2B9H9Me2)]

Abstract Treatment of a tetrahydrofuran solution of [NEt4][W(CCCtBu)(CO)2(η5-C2B9H9Me2)] with [Fe2(CO)9] affords the trimetal complex [NEt4][WFe2μ3-η3,η5-CHCC(tBu)C(O)C2B9H8Me2(CO)8], the structure of which has been established by X-ray diffraction. The anion has a core based on an essentially isosceles triangle of metal atoms [FeFe 2.663(3), WFe 2.811(2) and 2.829(2) A]. Each iron atom carries three CO groups, whereas the tungsten atom is co-ordinated by two such groups, and by the open face of a nido-icosahedral C2B9 cage. In the five-membered BBBCC ring forming the face of the cage, the boron atom occupying the β site with respect to the two carbon atoms is σ bonded to the carbon atom of a ketonic group [BC 1.57(3) A]. The latter in turn is linked to an allenyl fragment C(tBu)CCH [CC average 1.35(2) A, CCC 150(1)°] which spans the face of the WFe2 triangle. The terminal CH group is attached to the tungsten and to an iron atom [CW 2.25(1), CFe 1.96(1) A], and the central carbon is linked to the tungsten atom [CW 2.07 (1) A] and also to the second iron atom [CFe 2.05(1) A]. The latter is also bonded to the C(tBu) fragment [CFe 2.20(2) A] which in turn is connected to the ketonic group [C(tBu)C(O) 1.47(2) A] linking the μ3-C3 moiety to the cage. The NMR data (1H, 13C-1H, and 11B-1H) for the new cluster compound are reported and discussed.

Chemistry of polynuclear metal complexes with bridging carbene or carbyne ligands. Part 101. Synthesis of the compounds [WPt(µ-CC6H4Me-4)(µ-σ:ηx-C2BnHn–1Me2)(CO)2(PMe2Ph)2](x= 5, n= 9; x= 6, n= 10); crystal structures of an isomer of each complex

In acetone at ambient temperatures, the reagents [PtCl(Me)(PMe2Ph)2], TIBF4, and [NEt4][W(CC6H4Me-4)(CO)2(η5-C2B9H9Me2)] afforded [WPt(µ-CC6H4Me-4)(µ-σ:η5-C2B9H8Me2)(CO)2(PMe2Ph)2](two isomers), and a small amount of a salt formulated as [PtMe(PMe2Ph)3][W2Pt(µ-CC6H4Me-4)2(µ-σ:η5-C2B9H8Me2)(CO)4(η5-C2B9H9Me2)]. The structure of one isomer of the dimetal compound was determined by X-ray diffraction. The W–Pt bond [2.720(1)A] is spanned by the p-tolylmethylidyne group [W–µ-C 1.89(1), Pt–µ-C 2.14(1)A] and by a C2B9 fragment. The latter is co-ordinated to the W atom via the open pentagonal face of the nido-icosahedral cage, and bridges to the Pt atom through an exopolyhedral B–Pt σ bond [2.17(1)A]. This boron atom is in the β site with respect to the carbon atoms in the [graphic omitted] ring. In the other isomer it is the boron α to a carbon atom which forms the B–Pt bond. The reaction between the compounds [PtCl(Me)(PMe2Ph)2],TIBF4, and [NEt4][W(CC6H4Me-4)(CO)2(η6-C2B10H10Me2)] in thf (tetrahydrofuran) also yields two isomers of a dimetal species [WPt(µ-CC6H4Me-4)(µ-σ:η6-C2B10H9Me2)(CO)2(PMe2Ph)2]. The structure of the isomer formed in greatest yield (ca. 70%) was established by X-ray diffraction. The W–Pt bond [2.738(1)A] is bridged by the alkylidyne group [W–µ-C 1.92(1), Pt–µ-C 2.14(1)A] and by a C2B10 fragment. The non-planar [graphic omitted] face of the latter is η6 co-ordinated to the tungsten, but the cage also forms a B–Pt σ bond [2.15(1)A]. This linkage involves a boron atom of the B3 group α to a carbon, and correspondingly the other isomer is assigned a structure in which it is the [graphic omitted] atom of the hexagonal ring which bonds to platinum. The n.m.r. data (1H, 13C-{1H}, 11B-{1H}, and 31P-{1H}) for the new compounds are reported, and are in agreement with the structures proposed.

Synthesis and characterization of cationic dinuclear complexes of platinum with bridging hydrides; crystal structures of [Pt2(µ-H)2{But2P(CH2)3PBut2}2][BF4]2 and [Pt2(µ-H)2{(C6H11)2P(CH2)3P(C6H11)2}2][BF4]2

A series of diplatinum dications [Pt2(µ-H)2(L–L)2][BF4]2[L–L =(C6H11)2P(CH2)nP(C6H11)2, But2P(CH2)nPBut2, n= 2 or 3] with two chelating diphosphine and two bridging hydride ligands has been prepared by the elimination of ethene from the agostic alkyl complexes [PtEt(L–L)]+ or alkene–hydride complexes [PtH(C2H4)(L–L)]+, or by the reaction of the dihydride complexes [PtH2(L–L)] with an excess of HBF4·OMe2. The complexes have been characterized by multinuclear (1H, 31P and 195Pt) NMR spectroscopy and for [Pt2(µ-H)2{But2P(CH2)3PBut2}2][BF4]2 and [Pt2(µ-H)2{(C6H11)2P(CH2)3P(C6H11)2}2][BF4]2 by single-crystal X-ray crystallography. The latter complex has a structure in which the platinum and phosphorus atoms are coplanar whereas in the former the co-ordination planes of the platinum atoms are twisted with respect to each other by 36.6°. The twisting in [Pt2(µ-H)2{But2P(CH2)3PBut2}2][BF4]2 is ascribed to the steric pressure of the large diphosphine which destabilises the planar geometry. Significantly this complex is fluxional on the NMR time-scale at 290 K whereas the others are static and there is a shift in colour from yellow to red for the strained complex. The dinuclear species are useful synthetic precursors of the [PtH(L–L)]+ fragment, particularly when L–L is large. Thus [Pt2(µ-H)2{But2P(CH2)3PBut2}2]2+, which has the most sterically demanding diphosphine, reacts with alkenes [e.g. ethene (reversibly) or norbornene] to form mononuclear alkyl complexes with a three-centre, two-electron (agostic) bond.

Synthesis and reactivity of η3-γ-lactonyl complexes of molybdenum; crystal structures of [Mo{η3-OC(O)CHCHCH}(CO)2(η-C5Me5)], [Mo{η-2PhCH2NHCHCHCH(CO2H)}(CO)2(η5-C9H7)] and [Mo{η3-OC(O)CHCHCHCO}(NCMe)(CO)(η-C5H5)]

Reaction of 2-(trimethylsilyloxy)furan with the compounds cis-[Mo(NCMe)2(CO)2L][BF4](L =η-C5H5, η-C5Me5 or η5-C9H7) afforded the η3-γ-lactonyl complexes [Mo{η3-[graphic omitted]H}(CO)2L]. The structure of one of these species, [Mo{η3-[graphic omitted]H}(CO)2(η-C5Me5)], has been established by a single-crystal X-ray diffraction study, which confirmed that the γ-lactonyl moiety is bound to the molybdenum via three carbon atoms as an η3-allyl. Treatment of these lactonyl complexes with nucleophilic reagents (amines, methoxide) resulted in lactone ring opening and overall addition of the nucleophile to the γ-carbon of the lactone ring, rather than at the lactonyl carbonyl carbon atom as might have been expected. The product of the reaction between [Mo{η3-[graphic omitted]H}(CO)2(η5-C9H7)] and PhCH2NH2 has been structurally characterised by an X-ray diffraction study as the zwitterionic, η2-alkene complex [Mo{η2-PhCH2NHCHCHCH(CO2H}(CO)2(η5-C9H7)]. Similarly, [Mo{η3-[graphic omitted]H}(CO)2(η-C5H5)] and methoxide anion gives, after acidification, [Mo{anti-η3-(MeO)CHCHCH(CO2H)}(CO)2(η-C5H5)], in which the lactone ring has been cleaved to give an η3-allyl moiety ligating the metal centre. An extended Huckel molecular orbital calculation on [Mo{η3-[graphic omitted]H}(CO)2(η-C5Me5)] suggests that these reactions proceed via initial attack at the metal centre, followed by a rearrangement which effectively transfers the nucleophilic moiety to the γ-carbon of the lactone ring. Reaction of the η3-lactonyl complex [Mo{η3-[graphic omitted]H}(CO)2(η-C5H5)] with HBF4·Et2O resulted in a remarkable ring-enlargement reaction, in which a co-ordinated carbon monoxide formally inserts into the lactone carbon–oxygen bond to form the crystallographically characterised complex [Mo{η3-[graphic omitted]O}(NCMe)(CO)(η-C5H5)].