Complexes of the tripodal phosphine ligands PhSi(XPPh2)3 (X = CH2, O): synthesis, structure and catalytic activity in the hydroboration of CO2

The coordination chemistry of Fe2+, Co2+ and Cu+ ions was explored with the triphosphine and triphosphinite ligands PhSi{CH2PPh2}(3) (1) and PhSi{OPPh2}(3) (2), so as to evaluate the impact of the electronic properties of the tripodal phosphorus ligands on the structure and reactivity of the corresponding complexes. The synthesis and characterization of the complexes [ Fe(kappa(3)-PhSi{CH2PPh2}(3))(MeCN)(3)][OTf](2) (3) (OTf = O3SCF3), [ Fe(kappa(3)-PhSi{OPPh2}(3))(MeCN)(3)][OTf](2) (3'), [ Co(kappa(2)-PhSi{CH2PPh2}(3))Cl-2] (4), [ Co(kappa(3)-PhSi {OPPh2}(3))Cl-2] (4'), [ Cu(kappa(3)-PhSi{CH2PPh2}(3))Br] (5) and [Cu(kappa(3)-PhSi{OPPh2}(3))I] (5') were carried out. The crystal structures of 3, 3', 4, 4', and of the solvates 5.3THF and 5'center dot THF are reported. Complexes 3-5' were shown to promote the catalytic hydroboration of CO2 with (9-BBN)(2) (9-BBN = 9-borabicyclo [ 3.3.1] nonane). While the iron and cobalt complexes of the triphosphine 1 are more active than the analogous complexes with 2, the opposite trend is observed with the copper catalysts. Overall, the copper catalysts 5 and 5' are both more reactive and more selective than the Fe and Co catalysts, enabling the formation of the acetal H2C(OBBN)(2) with a high molar ratio of H2C(OBBN)(2) : CH3OBBN up to 92 : 8.