Mono- and di-dentate tertiary phosphine and monodentate tertiary phosphite derivatives of [Ru4H(CO)12BH2

Abstract

The reaction of the butterfly cluster [Ru4H(CO)12BH2] with a range of tertiary phosphines and diphosphines and with a large excess of trimethyl phosphite have been explored. Twenty-two derivatives of the general types [Ru4H(CO)12–x(PR3)xBH2](x= 1 or 2), [Ru4H(CO)12–x{P(OMe)3}xBH2](x= 2–4), [Ru4H(CO)11(L–L)BH2], [Ru4H(CO)10(L–L)BH2] and [{Ru4H(CO)11BH2}2{µ-(L–L)}](L–L = diphosphine) have been synthesised and characterised by mass spectrometry and IR and multinuclear NMR spectroscopies. The single-crystal structures of [Ru4H(CO)11(PPh3)BH2], trans-[Ru4H(CO)10{P(OMe)3}2BH2] and [Ru4H(CO)10(dppe)BH2]·CH2Cl2(dppe = Ph2PCH2CH2PPh2) have been determined. In [Ru4H(CO)11(PPh3)BH2] the PPh3 ligand occupies a wing-tip equatorial site. In [Ru4H(CO)10{P(OMe)3}2BH2] the two P(OMe)3 ligands are also in such sites and both the isomers in which these ligands are mutually cis or trans with respect to the cluster core are formed; the solid-state structure of the trans isomer has been confirmed. When the two phosphorus-donor atoms are provided in the form of a didentate ligand the sites of co-ordination depend upon the nature of the backbone of the ligand. In [Ru4H(CO)10(dppe)BH2], the dppe ligand bridges a Ruwing tip–Ruhing edge and two isomers are observed in solution; the solid-state structure of one isomer has been elucidated. Use of the diphosphine ligands allows the formation of linked dicluster species, and the competition for the formation of linked and monocluster species in which the ligand behaves in either a mono- or di-dentate fashion has been investigated. In the case of dppa [bis(diphenylphosphino)acetylene] and additional product when the ligand is in a four-fold excess is [Ru4H(CO)10(dppa)2BH2] in which both dppa ligands are pendant and co-ordinated to different wing-tip ruthenium atoms.