Massimino U. Pilotti

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 crystal structure of [Mo2FePt(μ-σ,σ′,σ″:η5-CC5H4)2(CO)4{HB(pz)3}2][HB(pz)3 = Hydrotris(pyrazol-1-yl)borate]; A complex derived from a 1,1′-ferrocene derivative with CMo(CO)2{HB(pz)3} substituents

Treatment of [Mo(CO) 6 ] in tetrahydrofuran, with 1,1′-dilithioferrocene in light petroleum, followed by (CF 3 CO) 2 O and tmeda (Me 2 NCH 2 CH 2 NMe 2 ) affords the ferrocene- substituted bis(alkylidynemolybdenum) complex [Mo 2 Fe(μ-σ, σ′,:η 5 -CC 5 H 4 ) 2 (O 2 CCF 3 ) 2 (CO) 4 (tmeda) 2 ]. The latter with K[HB(pz) 3 ] [HB(pz) 3 = hydrotris(pyrazol-1-yl)borate] in CH 2 Cl 2 gives [Mo 2 Fe(μ-σ,σ′:gh 5 -CC 5 H 4 ) 2 (CO) 4 {HB(pz) 3 } 2 ], which with [Pt(cod) 2 ] (cod = cyclo-octa-1,5-diene), in light petroleum saturated with ethylene, yields the tetranuclear metal complex [Mo 2 FePt(μ-σ,σ′,δ″:η 5 -CC 5 H 4 ) 2 (CO) 4 {HB(pz) 3 } 2 ]. The structure of this product was established by X -ray diffraction, and the results of this study are compared with those obtained for related compounds in which the two metal-metal bonds of an acyclic trimetal system, in this case MoPtMo, are each spanned by an alkylidyne group and semi-bridged by a carbonyl ligand.

Synthesis and crystal structures of the dimetal compounds [CoRh(CO)2(PPh3)(η4-C4Me4)(η5-C2B9H11)], [Rh2(CO)2(PPh3)2(η5-C2B9H11)], and [RhIrH(µ-σ : η5-C2B9H10)(CO)3(PPh3)2]

The salt [NEt4][Rh(CO)(PPh3)(η5-C2B9H11)](1) reacts with the complexes [Co(CO)2(NCMe)(η4-C4Me4)][PF6], [Rh2(µ-Cl)2(CO)4], and [IrCl(CO)2(NH2C6H4Me-4)] to afford, respectively, the dimetal compounds [CoRh(CO)2(PPh3)(η4-C4Me4)(η5-C2B9H11)](2), [Rh2(CO)2(PPh3)2(η5-C2B9H11)](3), and [RhIrH(µ-σ : η5-C2B9H10)(CO)3(PPh3)2](4). Complex (3) is also obtained in an unusual reaction involving addition of BH3·thf (thf = tetrahydrofuran) to (2). Treatment of (4) with K[BH(CHMeEt)3] in the presence of NEt4Cl gives the salt [NEt4][RhIr(µ-σ : η5-C2B9H10)(CO)3(PPh3)2], a process which can be reversed by addition of HBF4·Et2O to the latter. The structures of complexes (2)–(4) have been established by single-crystal X-ray diffraction studies. In (2) and (3) the metal–metal bonds [Co–Rh 2.746(3), Rh–Rh 2.692(3)A] are bridged by the C2B9H11 group such that the latter is η5co-ordinated to a rhodium atom while forming a three-centre two-electron B–H⇀M (M = Co or Rh) with the other metal centre. However, whereas in (2) it is a BH group which is α to a CH fragment in the pentagonal face of the cage which forms the B–H⇀Co bond, in (3), the B–H⇀Rh bond is formed by a BH group which is β to a CH group. In complex (3) both metal centres are co-ordinated by a CO and a PPh3 ligand. This is also true for the rhodium atom in (2), while the cobalt atom in the latter carries the tetra-methylcyclobutadiene ring and a CO group. Compound (4) has a Rh–Ir bond [2.781(1)A] bridged by a C2B9H10 moiety. The latter is η5 co-ordinated to the rhodium atom and forms an exopolyhedral B–Ir bond using a boron atom in the pentagonal face of the ligand which is α to a CH fragment. The iridium centre is ligated by two CO groups, and by a PPh3 and a hydrido ligand, while the rhodium atom carries a CO and a PPh3 group. The n.m.r. spectra (1H, 13C-{1H}, 31P-{1H}, and 11B-{1H}) of the new compounds are reported and discussed.

Synthesis of η4-1,3-diphosphacyclobutadiene(η5-1,2-dicarbaborane)rhodium complexes; crystal structures of the compounds [NEt4][Rh(η4-But2C2P2)(η5-C2B9H11)], [Rh{η4-But2C2P2Au(PPh3)}(η5-C2B9H11)], and [Rh{η4-But2C2P2Co-(CO)2(η4-C4Me4)}(η5-C2B9H11)]

Treatment of a thf (tetrahydrofuran) solution of K[Rh(PPh3)2(η5-C2B9H11)] with ButCP, followed by addition of NEt4Cl, affords the salt [NEt4][Rh(η4-But2C2P2)(η5-C2B9H11)](3), the structure of which has been established by X-ray diffraction. Compound (3) reacts with [AuCl(PPh3)] and with [Co(CO)2(NCMe)(η4-C4Me4)][PF6] to afford, respectively, the complexes [Rh{η4-But2C2P2Au-(PPh3)}(η5-C2B9H11)](4) and [Rh{η4-But2C2P2Co(CO)2(η4-C4Me4)}(η5-C2B9H11)](5). The structures of the products (4) and (5) have also been determined by X-ray diffraction. In all three compounds the rhodium is η5 ligated by a nido-icosahedral C2B9H11 fragment, and by a 1,3-diphosphacyclobutadiene group. Within the latter the P–C distances are equal, and the four-membered CPCP rings are close to planar. In the compounds (4) and (5) a phosphorus atom in the η4-But2CP2 group co-ordinates to the Au(PPh3) and the Co(CO)2(η4-C4Me4) groups, respectively. The n.m.r. data (1H, 13C-{1H}, 11B-{1H}, and 31P-{1H}) are reported, and where appropriate discussed.

Synthesis, crystal structure, and reactivity of the (η4-1,3-diphosphacyclobutadiene)(η5-1,2-dicarbaborane)rhodium complex [NEt4][Rh(η4-P2C2But2)(η5-C2B9H11)]

Tetrahydrofuran solutions of K[Rh(PPh3)2(η5-C2B9H11)] react with ButCP and NEt4Cl to afford the salt [NEt4][Rh(η4-But2 C2P2)(η5-C2B9H11)], which with [AuCl(PPh3)] and [Co(CO)2(NCMe)(η4-C4Me4)][PF6] yields the compounds [Rh(η4-But2C2P2MLn)(η5-C2B9H11)][MLn= Au(PPh3) or Co(CO)2(η4-C4Me4)]; all structurally identified by X-ray diffraction.

Chemistry of polynuclear metal complexes with bridging carbene or carbyne ligands. Part 95. Synthesis and crystal structures of [W2RuPt(µ-CC6H4Me-4)(µ3-CC6H4Me-4)(CO)6(PMe2Ph)(η-C5H5)2] and [W2Ru2Pt2(µ3-CC6H4Me-4)2(µ-CO)2(CO)9(η-C5H5)2]

Treatment of [W2Pt(µ-CC6H4Me-4)2(CO)4(η-C5H5)2] in thf (tetrahydrofuran) with [Ru(CO)4(η-C2H4)] in light petroleum affords the tetranuclear metal cluster compound [W2RuPt(µ-CC6H4Me-4)-(µ3-CC6H4Me-4)(CO)7(η-C5H5)2]. The latter with 1 equivalent of PMe2Ph gives [W2RuPt-(µ-CC2H4Me-4)(µ3-CC2H4Me-4)(CO)6(PMe2Ph)(η-C5H5)2], the structure of which has been established by X-ray diffraction. One p-tolylmethylidyne group caps three metal atoms WRuPt [W–Ru 2.743(1), W–Pt 2.729(1), and Ru–Pt 2.875(1)A] in an essentially symmetrical manner. The ruthenium atom carries two carbonyl groups and the phosphine ligand [Ru–P 2.271(4)A]. The tungsten atom is co-ordinated by a C5H5 ring and two CO ligands, but the latter asymmetrically bridge the W–Pt and W–Ru bonds [W–C–O 160(1) and 157(1)°, respectively]. The WRuPt triangle is linked through the Pt atom to a W(CC6H4Me-4)(CO)2(η-C5H5) fragment via a W–Pt bond [2.733(1)A] and a bridging µ-CC6H4Me-4 ligand [µ-C–W 1.92(1), µ-C–Pt 2.03(1)A]. One of the CO groups attached to the W atom weakly semi-bridges the W–Pt bond [W–C–O 170(1)°]. The reaction between [Ru(CO)4(η-C2H4)] and [W2Pt2(µ-CC6H4Me-4)(µ3-CC6H4Me-4)(CO)4(cod)–(η-C5H5)2](cod = cyclo-octa-1,5-diene) gives a hexanuclear metal cluster [W2Ru2Pt2-(µ3-CC6H4Me-4)2(µ-CO)2(CO)9(η-C5H5)], the structure of which has also been determined by X-ray diffraction. For descriptive purposes, five of the metal atoms [W(2)Ru(1)Ru(2)Pt(1)Pt(2)] may be regarded as occupying vertices of a ‘trigonal bipyramid’ but one in which two of the metal–metal bonds [Pt(1)⋯ Pt(2) 3.064(4), Ru(1)⋯ Pt(2) 3.259(2)A] are absent. Allowing for this, the ruthenium atoms occupy the apical sites, and the two platinum atoms and the tungsten atom occupy equatorial sites. The Pt(1) atom, in addition to being part of the open metal framework, is attached via a WPt bond [2.663(3)A] to an external W(CO)3(η-C5H5) fragment. One of the CO ligands on this W(1) atom asymmetrically bridges the W(1)Pt(1) linkage [W(I)–C–O 156(3), Pt(1)–C–O 122(2)°]. Both ruthenium atoms carry three terminal CO groups. The Pt(2) atom, ligated only by two of the metal atoms [W(2) and Ru(2)] in the framework, carries a terminal CO group, and the Pt(2)–Ru(2) bond is bridged by a CO ligand [Ru(2)–C–O 136(3), Pt(2)–C–O 143(4)°]. The W(2) atom carries a C5H5 ring. Both p-tolylmethylidyne groups occupy triply bridging sites. These are on the same side of the Pt(1)W(2)Pt(2) plane, one ligand caps the W(2)Ru(1)Pt(1) triangle, the other spans the atoms Pt(2), W(2), Ru(1). The n.m.r. spectra of the new mixed-metal clusters are reported and discussed.

Synthesis and crystal structures of the complexes [RhPt(µ-H)(µ-CO)(PEt3)2(PPh3)(η5-C2B9H11)] and [RhPt{σ-C(C6H4Me-4)C(C6H4Me-4)H}(CO)(PEt3)(PPh3)(η5-C2B9H11)]

The reaction between [NEt4][Rh(CO)(PPh3)(η5-C2B9H11)] and [PtCl(H)(PEt3)2] in acetone, in the presence of TIBF4, affords the dimetal compound [RhPt(µ-H)(µ-CO)(PEt3)2(PPh3)(η5-C2B9H11)]. The structure of this complex has been established by an X-ray diffraction study. The Rh–Pt bond [2.734(2)A] is bridged by a hydrido ligand [Rh–H 1.7(2), Pt–H 1.8(2)A] and by a carbonyl group [Rh–CO 1.99(1), Pt–CO 1.99(1)A; Rh–C–O 133(1), Pt–C–O 141(1)°]. The platinum atom carries the two PEt3 ligands [Pt–P 2.275(4) and 2.335(4)A], while the rhodium atom is co-ordinated by the PPh3 molecule [Rh–P 2.257(4)A] and the five atoms [graphic omitted] in the pentagonal face of the nido-C2B9H11 cage. Treatment of this dimetal compound with the alkynes RCCR (R = Ph or C6H4Me-4) in tetrahydrofuran at room temperature affords the complexes [RhPt{σ-C(R)C(R)H}(CO)(PEt3)(PPh3)(η5-C2B9H11)]. An X-ray diffraction study on the species with R = C6H4Me-4 revealed the following structural features. The Rh–Pt bond [2.762(1)A] is bridged by the C2B9H11 cage such that the latter is η5 co-ordinated to the rhodium atom while forming an exopolyhedral bond to the platinum via a three-centre B–H ⇀ Pt linkage. The boron atom involved lies in the pentagonal face of the cage ligating the rhodium, and is in the β site with respect to the two carbon atoms. The rhodium atom is co-ordinated by a PPh3[Rh–P 2.294(2)A] and a CO [Rh–CO 1.845(8)A] group. The platinum atom carries the PEt3 ligand [Pt–P 2.221(2)A] and a σ bonded cis-C(C6H4Me-4)C(C6H4Me-4)H vinyl group [Pt–C 2.036(7)A]. N.m.r. data (1H,13C-{1H},31P-{1H}, and 11B-{1H}) for the compounds are reported and discussed.

Chemistry of polynuclear metal complexes with bridging carbene or carbyne ligands. Part 84. Carbaborane tungsten–platinum complexes having a µ-CC6H3Me2-2,6 ligand; crystal structures of [WPt(µ-CC6H3Me2-2,6)(CO)n(PEt3)(µ-σ:η5-C2B9H8Me2)](n= 2 or 3)

The reaction between the salts [PtH(Me2CO)(PEt3)2][BF4] and [NEt4][W(CC6H3Me2-2,6)(CO)2(η5-C2B9H9Me2)] in acetone at low temperature (ca. –30 °C) affords the dimetal compound [WPtH(µ-CC6H3Me2-2,6)(CO)2(PEt3)(η5-C2B9H9Me2)], in which the carbaborane ligand forms a B–H⇀Pt three-centre bond by employing a BH group in the pentagonal face of the cage. This product readily affords, via loss of hydrogen, the complex [WPt(µ-CC6H3Me2-2,6)(CO)2(PEt3)(µ-σ:η5-C2B9H8Me2)] as a mixture of two isomers. The structure of the major isomer (ca. 80%) has been established by X-ray diffraction. The W–Pt bond [2.728(1)A] is asymmetrically bridged by the CC6H3Me2-2,6 group [µ-C–W 1.88(2), µ-C–Pt2.15(2)A]. Indeed with a W–µ-C–C1(C6H3) angle of 175(1)° these three atoms are nearly linear. The carbaborane ligand has undergone ‘slippage’ along the W–Pt vector to accommodate formation of a direct exopolyhedral B–Pt σ bond [2.01(2)A]. This linkage involves the central boron in the [graphic omitted] face of the icosahedral fragment η5 bonded to tungsten. The PEt3 ligand attached to the platinum atom [Pt–P, 2.251(7)A] is transoid to the µ-C and W atoms [µ-C–Pt–P, 160.6(4)°, W–Pt–P 155.9(1)°]. The n.m.r. data (1H, 13C-{1H}, 11B-{1H}, and 31P-{1H}) are in accord with the structure established by the X-ray diffraction study. Similar data for the minor isomer reveal that this species had a structure in which the B–Pt σ bond involves a boron atom [graphic omitted] in the face of the cage, adjacent to a CMe group. The two isomers may be separated by column chromatography, but solutions equilibrate on standing. Formation of the major isomer from [WPtH (µ-CC6H3Me2-2,6)(CO)2(PEt3)(η5-C2B9H9Me2)] can be partially reversed by treating solutions of the former with hydrogen. Mechanisms are proposed for these various transformations based in part on deuteriation studies employing [PtD(Me2CO)(PEt3)2][BF4] as a precursor to the W–Pt species. The compound [WPt(µ-CC6H3Me2-2,6)(CO)2(PEt3)(µ-σ:η5-C2B9H8Me2)](major isomer) is relatively inert to the addition of ligands at the formally 14-electron platinum centre, presumably due to the presence of the bulky xylyl group. However, reactions very readily occur with rod-like ligands (L = CO or CNBut) to give the compounds [WPt(µ-CC6H3Me2-2,6)(CO)2(PEt3)(L)(µ-σ:η5-C2B9H8Me2)]. Indeed the tricarbonyl complex is a major constituent of the mixture of products obtained by treating the complex [NEt4][W(CC6H3Me2-2,6)(CO)2(η5-C2B9H9Me2)] with [PtH(Me2CO)(PEt3)2][BF4]. An X-ray study of the carbon monoxide adduct revealed a structure similar to the precursor with parameters W–Pt, 2.728(1),µ-C–W 1.89(1), µ-C–Pt 2.29(1), B–Pt 2.16(1)A, W–µ-C–C1(C6H3) 160.0(8), and P–Pt–W 138.5(1)°. The significantly lower W–µ-C–C1(C6H3) angle (ca. 160°) compared with that in the precursor is presumably a consequence of the presence of the additional CO ligand terminally bound to the platinum and cisoid to the alkylidyne group [µ-C–Pt–CO 83.5(4)°].

Chemistry of polynuclear metal complexes with bridging carbene or carbyne ligands. Part 112. Synthesis of rhenium–rhodium complexes; crystal structure of [ReRh{µ-σ,η5-C2B9H7(CH2C6H4Me-4)Me2}(CO)4(η-C5H4Me)]

Treatment of [NEt4][Rh(CO)2(η5-C2B9H9Me2)] in CH2Cl2 with [Re(CC6H4Me-4)(CO)2(η-C5H4Me-4)]-[BCl4] affords the dimetal complex [ReRh{µ-σ,η5-C2B9H7(CH2C6H4Me-4)Me2}(CO)4(η-C5H4Me)]. The structure was established by X-ray diffraction. The Re–Rh bond [2.888(1)A] is spanned by the C2B9H7(CH2C6H4Me-4)Me2 fragment. The open pentagonal face of the C2B9 cage is η5 co-ordinated to the rhodium, and there is an exopolyhedral B–Re [2.17(2)A]σ bond involving a boron atom in the α site with respect to the carbon atoms in the [graphic omitted] ring; the boron atom in the β site [graphic omitted] carries the CH2C6H4Me-4 substituent. The rhenium and rhodium atoms are each ligated by two terminally bound CO molecules, and the rhenium is also co-ordinated by the η-C5H4Me group. The related complexes [ReRh{µ-σ,η5-C2B9H7(CH2C6H4Me-4)Me2}(CO)3L(η-C5H5)](L = CO or PMe2Ph) have also been prepared. In contrast with the aforementioned results the complex [Mn(CC6H4Me-4)(CO)2(η-C5H4Me)][BCl4] reacts with [NEt4][Rh(CO)(PPh3)(η5-C2B9H9Me2)] and [NEt4][Rh(cod)(η5-C2B9H9Me2)](cod = cycloocta-1,5-diene) to give the mononuclear rhodium species [Rh{σ,η5-H(C6H4Me-4)C2B9H9Me2}(CO)(PPh3)] and [Rh{σ,η5-CH(C6H4Me-4)C2B9H8Me2}(cod)], respectively. The NMR data (1H, 13C-{1H}, 11B-{1H}] for the new complexes are reported and discussed.

Chemistry of polynuclear metal complexes with bridging carbene or carbyne ligands. Part 102. Alkylidyne ligand migration from manganese to a rhodacarbaborane cluster; crystal structure of [Rh{σ,η5-CH(C6H4Me-4)-C2B9H10}(CO)(PPh3)]

Treatment of CO-saturated CH2Cl2 solutions of the salts [X][Rh(CO) L(η5-C2B9H9R′2)][X = NEt4, L = PPh3, R′= H; L = CO, R′= Me; X = N(PPh3)2, L = CO, R′= H] with the reagents [Mn(CR)-(CO)2(η-C5H4Me)][BCl4](R = C6H4Me-4 or C6H3Me2-2,6) affords the rhodium complexes [Rh{σ,η5-CH(R)C2B9H8R′2}(CO)L](R = C6H4Me-4, R′= H, L = PPh3 or CO; R = C6H4Me-4, R′= Me, L = CO; R = C6H3Me2-2,6, R′= H, L = PPh3). The structure of the compound [Rh{σ,η5-CH(C6H4Me-4)C2B9H10}(CO)(PPh3)] was established by X-ray diffraction. The rhodium atom is ligated by the CO and PPh3 groups [Rh–CO 1.854(3), Rh–P 2.302(1)], and by the CH(C6H4Me-4)C2B9H10 fragment. In the latter the CH(C6H4Me-4) moiety forms a bridge between the rhodium [Rh–C 2.374(3)A] and a boron atom [B–C 1.501 (4)A] in the pentagonal face of the cage. This boron atom is in the β site ([graphic omitted]) with respect to the carbon atoms, and all the atoms of the ring are bonded to the rhodium, but the connectivities are somewhat asymmetric [Rh–C 2.373(3) and 2.341 (3)A, Rh–B 2.205(3), 2.165(3), and 2.237(3)A]. In the molecule the PPh3 and C6H4Me-4 groups are transoid to one another about the Rh–CH(C6H4Me-4)σ bond, but n.m.r. studies on solutions reveal the presence of a second isomer with a cisoid configuration for the PPh3 and C6H4Me-4 groups. Reactions of the rhodium compounds with K[BH(CHMeEt)3] in tetrahydrofuran led to rupture of the Rh–C(H)R σ bonds and formation, in the presence of NEt4Cl, of the salts [NEt4][Rh(CO)L{η5-C2B9H8(CH2R)R′2}](L = PPh3, R = C6H4Me-4 or C6H3Me2-2,6, R′= H; L = CO, R = C6H4Me-4, R′= Me). The n.m.r. data (1H, 13C-{1H}, 31P-{1H}, and 11B-{1H}) for the new complexes are reported and discussed.