Water-soluble alkyl phosphine complexes of ruthenium and rhodium : an investigation into their different reactivity in solution

• Main Author: Higham, Lee
• Published: University of East Anglia 2000
• Subjects: 546; Inorganic chemistry
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.327496

The reaction ofP(CH20H)3 and P(C6HS)(CH20ffll with RuCh in methanol yielded the complexes all trans-[RuCh(P(CH20H)3)2(P(CH20H)2H)2] (1) and all trans-[RuCh(P(4Hs)(CH20H)2h(P(C~s)(CH20H)Hh] (2) respectively. The reaction products were characterised by NMR and IR spectroscopy, X-ray crystallography and elemental analysis. Both complexes demonstrated a high degree of hydrogen-bonding interactions however the ratio of hydrophobic phenyl groups to hydrophilic hydroxymethyl moieties in 2 made the complex insoluble in most solvents. Complexes 1 and 2 show two equivalents of formaldehyde were eliminated to form two secondary phosphine ligands. The mixed tertiary-secondary phosphine complexes 1 and 2, from P(CH20H)3 and P(4HS)(CH20H)2 therefore demonstrate a reactivity of ruthenium towards phosphines possessing a hydroxymethyl functionality. The reaction mechanism appeared to be the same for both 1 8)1d 2. The reaction of P(CH20H)3, P(~S)(CH20H)2 and P«CH2)30H)3 with [RhCI(cod)h in an aqueousldichloromethane biphasic medium yielded [RhH2(p(CH20H)3)4r (3), [RhH2(P(C6Hs)(CH20 H)2)4r (4) and [Rh(P(~5)(CH20Hh)4r (5), and [Rh(P«CH2)30H)3)4t (6) respectively. The latter cation did not form the corresponding dihydride in aqueous solution, although [RhH2(p«CH2)30 H)3)41+ (7) was readily formed by reaction with dihydrogen. The protic nature of3 and 4 was illustrated by the H-D exchange observed in d2-water. Indeed, the dideuteride analogues of3 and 4 were easily prepared by using d2-water in the biphasic reaction with [RhCI( cod) h. In contrast, the dideuteride cation [RhD2(p«CH2)30H)3)4t could not be prepared in this manner, nor was any H-D exchange observed. In aqueous solution no reaction was observed between the dihydrides and C02, but treatment with CO yielded the I8-electron, five-coordinate dicarbonyl cations [Rh(CO)2(P(CH20H)3)3t (8), [Rh(CO)2(P(C6Hs)(CH20H)2)3t (9), and [Rh(CO)2(P«CH2)30H)3)3r (10).