Water-soluble hydroxyalkylated phosphines: examples of their differing behaviour toward ruthenium and rhodium

The reaction of P(CH2OH)3 (I) and PPh(CH2OH)2 (II) with RuCl3 in MeOH eliminates two equiv. of formaldehyde to yield the mixed tertiary and secondary phosphine complexes all-trans-[RuCl2(P(CH2OH)3)2(P(CH2OH)2H)2] (1) and [RuCl2(PPh(CH2OH)2)2(PPh(CH2OH)H)2] (2), resp. There is a high degree of H-bonding interactions between the hydroxymethyl groups in 1 and 2, although the Ph groups of the latter reduce the extent of the network compared to 1. The generation of these mixed secondary and tertiary phosphine complexes is unprecedented. Under the same reaction conditions, the tris(hydroxypropyl)phosphine III formed no Ru complex. The reaction of P(CH2OH)3, PPh(CH2OH)2 and P{(CH2)3OH}3 with [RhCl(1,5-cod)]2 in an aq./CH2Cl2 biphasic medium yielded [RhH2(P(CH2OH)3)4]+ (3), [RhH2(PPh(CH2OH)2)4]+ (4) and [Rh(PPh(CH2OH)2)4]+ (5) and [Rh(P{(CH2)3OH}3)4]+ (6), resp. Treating 5 with dihydrogen rapidly gave 4. The hydroxypropyl compd. 6 formed the corresponding dihydride much more slowly in aq. soln., although [RhH2(P{(CH2)3OH}3)4]+ (7) was readily formed by reaction with dihydrogen. Two sep. reaction pathways are therefore involved; for P(CH2OH)3 and to a lesser extent PPh(CH2OH)2, the hydride source in the product probably is the aq. solvent or the hydroxyl protons, while for P{(CH2)3OH}3 an oxidative addn. of H2 is favored. The protic nature of 3 and 4 was illustrated by the H-D exchange obsd. in d2-H2O. Dihydrides 3 and 4 reacted with CO to yield the dicarbonyl cations [Rh(CO)2(P(CH2OH)3)3]+ (8) and [Rh(CO)2(PPh(CH2OH)2)3]+ (9). The analogous expt. with [RhH2(P{(CH2)3OH}3)4]+ resulted in phosphine exchange, although the authors' exptl. evidence points to the possibility of more than one fluxional process in soln.