Brian R. Lloyd

Benzyne complexes of ruthenium: Models for dissociative chemisorption of benzene on a metal surface. Crystal structures of [Ru4(CO)10(μ-CO)(μ4-PR)(μ4-η4-C6H4)] (R = Ph and CH2NPh2), [Ru5(CO)13(μ4-PPh)(μ5-η6-C6H4)] and [Ru6(CO)12(μ4-PMe)2(μ3-η2-C6H4)2]

Abstract Heating a solution of [Ru 3 (CO) 11 (PPh 3 )] in toluene gives the μ 3 -, μ 4 - and μ 5 -benzyne complexes [Ru 3 (CO) 7 (μ-PPh 2 ) 2 (μ 3 -η 2 -C 6 H 4 )] ( 1a ) (33%), [Ru 4 (CO) 10 (μ-CO)(μ 4 -PPh)(μ 4 -η 4 -C 6 H 4 )] ( 2a ) (50%) and [Ru 5 (CO) 13 (μ 4 -PPh)(μ 5 -η 6 -C 6 H 4 )] ( 3a ) (7%), respectively. The structures of 2a and 3a have been established by X-ray diffraction, revealing that the benzyne in each case is bound to a square of ruthenium atoms by CRu σ-bonds to two adjacent rutheniums, and by η 2 -interactions to the other two atoms of the Ru 4 square. In 3a there is also η 2 -co-ordination to a third ruthenium atom, so that there is η 6 -co-ordination overall. The five metal atoms of 3a are arranged like a step site on a metal (111) surface and the complex can be viewed as a model for the aftermath of benzene CH activation on such a surface. The thermolysis of [Ru 3 (CO) 11 (PPh 2 CH 2 NPh 2 )] gives the μ 4 -PCH 2 NPh 2 analogue 2b of 2a , while from [Ru 3 (CO) 11 (PPh 2 Me)] the new cluster [Ru 6 (CO) 12 (μ 4 -PMe) 2 (μ 3 -η 2 -C 6 H 4 ) 2 ] ( 11 ) is isolated in 11% yield. The structures of 2b and of 11 have been determined by X-ray diffraction; 11 contains two μ 3 -benzyne ligands bound to triruthenium faces of an Ru 6 P 2 cluster. Thermolysis of the tritolylphosphine complexes [Ru 3 (CO) 11 (PAr 3 )](Ar = C 6 H 4 - m -Me or C 6 H 4 - p -Me) affords only analogues of 1 and 2 , containing in each case the μ-C 6 H 3 -4-Me ligand. Heating [Ru 3 (CO) 11 (AsPh 3 )] gives low yields of the arsenic analogues of 2 and 3 in addition to the major product [Ru 2 (CO) 6 (μ-AsPh 2 ) 2 ] (65%). The fluxional behaviour of complexes 1 and 2 , involving benzyne rotation on Ru 3 and Ru 4 centres, respectively, is discussed, and pathways for the formation of 1, 2 and 3 are proposed.

Co-ordination of benzyne at tetra- and pentra-ruthenium centres: a model for dissociative chemisorption of benzene on a stepped metal (111) surface

Heating [Ru3(CO)11(PPh3)] in toluene yields complexes [Ru4(CO)11(µ4-η4-C6H4)] and [Ru5(CO)13(µ4-PPh)(µ5-η6-C6H4)], structurally identified by X-ray diffraction, in which benzyne is co-ordinated at tetra-and penta-ruthenium centres respectively; the latter provides a model for the dissociative chemisorption of benzene at a step site on a metal (111) surface.

Reactions of [Fe2(CO)6(μ-CO)(μ-dppm)] with alkynes: Stepwise synthesis of tropone at a dinuclear metal centre☆

Abstract The di-iron complex [Fe2(CO)6(μ-CO)(μ-dppm)] [ 1 ; dppm = bis(diphenylphosphino)methane ] reacts with alkynes R1CCR2 under UV irradiation to produce dimetallacyclopentenone complexes [Fe2(CO)5{μ-σ:η3-CR1CR2C(O)}(μ-dppm)] (2a-e; R1 = R2 = H, Me or Ph; R1 = H, R2 = Me or Ph). The complexes exist in two isomeric forms in which the diphosphine ligand is either cis or trans with respect to the organic ligand. In the cis isomers of complexes 2 the R1 site is occupied by hydrogen, while in the trans isomers the R1 site is occupied by Me or Ph, suggesting that steric factors control the geometry. The molecular structure of cis-[Fe2(CO)5{μ-σ:η3-CHCHC(O)}(μ-dppm)] (2a) has been elucidated by X-ray diffraction. The complex exists in the solid state as a mixture of enantiomers, shown by variable temperature NMR spectroscopy to interconvert in solution via ethyne migration from one CO ligand to another. Further reaction of 2a with ethyne affords [Fe2(CO)4{μ-σ,σ′:η2,η2′-CHCHC(O)CHCH}(μ-dppm)] (3) and [Fe2(CO)4{μ-η3:η3′-C6H6C(O)}(μ-dppm)] (4) stepwise, containing and three molecules of ethyne, respectively. X-ray diffraction studies show that 3 is a pentadienone “fly-over bridge” complex and that 4 is a complex of tropone, stabilized by a weak intramolecular CH…O hydrogen bond. Addition of diphenylacetylene to trans-[Fe2(CO)5{μ-σ:η3-CPhCPhC(O)}(μ-dppm)] (2e) affords the “ferrole” complex trans-[Fe2(CO)5{μ-σ,σ′:η4-C4Ph4}(μ-dppm)] (5), also crystallographically characterized. The different pathways for alkyne linking with 2a and 2e are traced to steric factors, arising from the different orientations of the diphosphine and organic ligands in the two species.

Generation of a µ3-vinylidene ligand via step-wise cleavage of 1,1-bis(diphenylphosphino)ethylene at di- and tri-iron centres

Through a sequence of thermally- and photochemically-induced steps the 1,1-bis(diphenylphosphino)ethylene ligand in [Fe2(CO)7{µ-(Ph2P)2CCH2}] or [Fe3(CO)10{µ-(Ph2P)2CCH2}] is fragmented to generate the µ3-vinylidene complex [Fe3(CO)6(µ-CO)(µ-PPh2)2(µ3-CCH2)]; the structures of the latter and of two ‘phospha-allene’ precursors [Fe2(CO)5(µ-PPh2)(µ-Ph2PCCH2)] and [Fe3(CO)9(µ-PPh2)(µ3-Ph2PCCH2)] have been established by X-ray diffraction.

Co-ordination chemistry at a triply bridging site of [Pd3(µ3-CO)(µ-Ph2PCH2PPh2)3]2+: the structure of the chloride adduct

The selective attachment of halide ions to a triply bridging site in the complex cation [Pd3(µ3-CO)(µ-dppm)3]2+(dppm = Ph2PCH2PPh2) has been established and the structure of the chloride adduct determined; the chloride ligand is very weakly bound to the Pd3 unit and is shielded by a ring of phenyl groups from the dppm ligands.

Reactivity of bis(diphenylphosphino) methane at a di-iron centre: thermally induced rearrangements of dimetallacyclopentenone complexes [Fe2(CO)5{μ-σ:η3-C(O)CRCr}(μ-dppm)]

Abstract In toluene at 100°C the dimetallacyclopentenone complex [Fe2(CO)5{μ-σ:η3-C(O)CHCH}(μ-dppm)] (1a) isomerises to the μ-vinyl complex [Fe2(CO)6{μ-C(CH2)P(Ph2)CH2PPh2}] (2) via intramolecular nucleophilic attack of phosphorus on a carbon of the metallacycle, with an associated 1,2-hydrogen shift and CC bond cleavage. On further heating to 110°C, 2 in turn is transformed to isomeric [Fe2(CO)6−{μ-C(CH2Ph)P(Ph2)CH2PPh}] (3), arising from transfer of a phenyl group from phosphorus to carbon, and the complex [Fe2(CO)5−{μ-Ph2PCH2P(Ph)C6H4C(CH3)}] (4a), resulting from more complex rearrangement. Heating the complexes [Fe(CO)5−{μ-σ:η3(C(O)CRCH}(μ- dppm)] (R = Me (1b), Ph (1c)) gave only [Fe2(CO)2{μ-Ph2PCH2P(Ph)C6H4C(CH2R)}] (4b, 4c), the likely intermediates analogous to 2 and 3 not being detectable. The structures of 2, 3 and 4c were established by X-ray diffraction, providing an insight into the molecular manoeuvres involved in the rearrangements. In contrast to the ready thermolysis of 1a-c, in which the diphosphine and organic moieties lie cis to one another, the analogous trans complexes [Fe(CO)5{μ-σ:C(O)CRCR}(μ-dp pm)] (R = Me (1d), Ph (1e)) are stable in refluxing toluene, partly attributable to the inability of phosphorus to attack the distant metallacycle.

Structural observation of bis(diphenylphosphino)methane reactivity at a di-iron centre: crystal structures of isomeric [Fe2(CO)5(µ-CHCHCO){µ-P(Ph2)CH2PPh2}], [Fe2(CO)6{µ-C(CH2)P(Ph2)CH2PPH2}], and [Fe2(CO)6{µ-C(CH2Ph)P(Ph2)CH2PPh}]

X-Ray diffraction studies have elucidated the molecular rearrangements involved in the fluxionality of the complex [Fe2(CO)5(µ-CHCHCO){µ-P(Ph2)CH2PPh2}] and in its isomerisation, via migration of one phosphorus of the bis(diphenylphosphino)methane ligand from iron to carbon, to give [Fe2(CO)6{µ-C(CH2)P(Ph2)CH2PPh2}], which in turn isomerises through phenyl migration from phosphorus to carbon, yielding [Fe2(CO)6{µ-C(CH2Ph)P(Ph2)CH2PPh}].

A fluxional tetraplatinum cluster: solution and solid state structure of the cation [Pt4(µ-H)(µ-CO)2(µ-Ph2PCH2PPh2)3(Ph2PCH2PPh2)]+

The 58-electron cationic cluster complex [Pt4(µ-H)(µ-CO)2(µ-dppm)3(dppm-P)]+, dppm = Ph2PCH2PPh2, has been characterized in solution by n.m.r. spectroscopy and in the solid by X-ray analysis of the PF6– salt; the cation displays novel fluxionality with rapid rotation of a µ-H below and a µ-Pt(CO)2(dppm-P) unit above a Pt3(µ-dppm)3+ triangle.

Bis(dialkylphosphino)methane complexes of palladium(II) and the molecular structure of [Pd2Cl3(µ-PriPCH2PPri2)(µ-Pri2PCH2PHPri)]·2CHCl3 containing an unusual phosphidophosphine bridging ligand

The mononuclear chelate complexes [PdX2(R2PCH2PR2)](X = CF3CO2 or Cl; R = Me, Et, or Pri) have been prepared and characterized spectroscopically. Reaction of [PdCl2(PhCN)2] with Pri2PCH2PHPri gave a novel binuclear complex, [ Pd2Cl3(µ-PriPCH2PPri2)(µ-Pri2PCH2PHPri)], with the phosphidophosphine ligand in an unusual bridging mode. This complex was characterized by 1H and 31P n.m.r. spectroscopy and by X-ray crystal-structure analysis of its trichloromethane solvate [triclinic, space group P, a= 8.744(2), b= 11.483(1), c= 20.108(4)A, α= 103.49(1), β= 97.15(2), γ= 91.11(2)°, Z= 2, R= 0.035 for 5 918 symmetry-independent reflections with I 3σ(I)].