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 Ru_{wing tip}–Ru_hing 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.