Synthesis, reactivity, and crystal and molecular structures of [µ-1,4-bis(diphenylphosphino)butane]-dicarbonylbis-(ηcyclopentadienyl)-dirhodium(I)

Abstract

The title compound (1) was obtained from the reaction of [Rh(η-C₅H₅)(CO)₂] with 1,4-bis(diphenylphosphino)-butane (dppb). An X-ray structure determination of (1) has shown that it crystallises in space group P with a= 7.650(2), b= 9.323(3), c= 13.253(3)Å, α= 106.1(1), β= 100.1(1), γ= 93.4(1)°. Its structure has been determined from three-dimensional X-ray data collected by counter methods. The final R factor obtained by full-matrix least-squares refinement of 2 022 reflections was 0.051. The crystal consists of discrete dimeric molecules of symmetry held together by the bridging dppb group. The centrosymmetrically related rhodium atoms occupy the centre of a triangle at the vertices of which are planarly disposed a terminal carbonyl group, the centre of the cyclopentadienyl ring, and the phosphorus of the dppb ligand.

The reactions of the binuclear rhodium(I) complex (1) with small molecules have been studied. The dinitrosyl rhodium complex [Rh₂(µ-dppb)(η-C₅H₅)₂(NO)₂][PF₆]₂ was obtained by treating (1) with [NO][PF₆]. Complex (1) reacts with halogens to give the rhodium(III) dicationic compounds [Rh₂(µ-dppb)(η-C₅H₅)₂(CO)₂-X₂]X₂(X = Cl, Br, or I). The diacetyl derivative [Rh₂(µ-dppb)(η-C₅H₅)₂(COMe)₂l₂] is the product of the reaction of (1) with Mel; the dicationic rhodium(III) compounds [Rh₂(µ-dppb)(η-C₅H₅)₂(CO)₂(CH₂CN)₂]²⁺ and [Rh₂(µ-dppb)(η-C₅H₅)₂(CO)₂Me₂]²⁺ are obtained in the reactions with CH₂CICN and [OMe₃][PF₆]. Mercury(II) chloride forms with (1) the adduct [Rh₂(µ-dppb)(η-C₅H₅)₂(CO)₂(HgCl₂)₂]. The i.r. and ¹H n.m.r. spectra of the new compounds are discussed.