η5-Cyclopentadienylrhodium(I) complexes containing diphosphines and their reactions with the electrophiles H+ and Me+. Crystal and molecular structure of [Rh(η-C5H5)(CO)(Ph2PCH2PPh2)], a complex with a unidentate bis(diphenylphosphino)methane ligand

Abstract

The compounds [Rh(η-C₅H₅)(dppm)(CO)](2), [Rh(η-C₅H₅)(dppe)](3), and [Rh(η-C₅H₅)(dppp)](4) were obtained from the reactions of [Rh(η-C₅H₅)(CO)₂](1) with bis(diphenylphosphino)methane (dppm), 1,2-bis(diphenylphosphino)ethane (dppe), and 1,3-bis(diphenylphosphino) propane (dppp) respectively. The X-ray structure determination of (2) shows it to crystallize in the space group P2₁/n with unit-cell dimensions a= 13.734(4), b= 9.771(3), c= 20.440(8)Å, β= 103.9(1)°, and Z= 4. R′= 0.05 for 2 864 observed reflections. Some relevant bond distances are Rh–(centroid of C₅H₅ ring)= 1.932, Rh–P = 2.238(2), and Rh–C(carbonyl)= 1.806(8)Å. The bonding of the dppm ligand is, unusually, unidentate to the metal. The reactions of (2), (3), (4), and of the previously reported complex [{Rh(η-C₅H₅)(CO)}₂(µ-dppb)](6)[dppb = 1,4-bis(diphenylphosphino) butane], with the electrophilic agents H⁺ and Me⁺ have been studied. Complex (3) reacts with HBF₄ to give the cationic hydride [Rh(η-C₅H₅)H(dppe)]BF₄(5); in the same reaction (4) and (6) gave unstable products. The protonic attack of HCl on (3), (4), and (6) results in the formation of compounds devoid of co-ordinated cyclopentadienyl ion. The binuclear complex [{Rh(CO)(µ-Cl)}₂(µ-dppb)](7) was the product of the reaction of (6) with HCl; for this reaction a possible mechanism is proposed. The reactions of HCl with (3) and (4) are more complex and mixtures containing [{Rh(P–P)Cl}_n] and the rhodium(III) hydride [{RhH(P–P)Cl₂}_n](n= 1 or 2, P–P = dppe or dppp) were isolated. The compound [{Rh(dppe)Cl}₂] was formed by the reaction of (5) with [AsPh₄]Cl. The electrophilic attack of Mel on (2) takes place either at the metal or at the unco-ordinated phosphorus atom of dppm and the reaction product is [Rh(η-C₅H₅)(COMe)I(Ph₂PCH₂PMePh₂)]I. Mel reacts with (3) and (4) to give [Rh(η-C₅H₅)Me(dppe)]I and [Rh(η-C₅H₅)Me(dppp)]I, which are very unstable in solution.