Some rhenium hydride complexes with tetradentate phosphine co-ligands: the crystal structure of Re(H 2BEt 2)( racemic-tetraphos)

Abstract

ReH 5(PMePh 2) 3 reacts with P(CH 2CH 2PPh 2) 3 (PP 3) in the absence of solvent at 180° to give ReH(PMePh 2)(PP 3). Under similar conditions, ReCl 3(PMePh 2) 3 reacts with tetraphosphine ligands PP 3 or commercially available P 4 (Ph 2PCH 2CH 2P(Ph)CH 2CH 2P(Ph)CH 2CH 2PPh 2) to produce ReCl 3(PP 3) and ReCl 3(P 4), respectively. Treatment of ReCl 3(PP 3) with NaBH 4 yielded ReH 3(PP 3), which is converted into [ReH 4(PP 3)] + when protonated. Treatment of ReCl 3(P 4) with NaBH 4 in MeOH/benzene produced a mixture of ReH 3( meso-P 4) and ReH 3( rac-P 4). On the other hand, a mixture of ReH 3( meso-P 4) and the novel complex Re(BH 2Et 2)( rac-P 4) was obtained when ReCl 3(P 4) was treated with an old sample of LiBHEt 3 (actually containing LiBEt 4/LiBH 2Et 2) in THF. Protonation of ReH 3( meso-P 4) produced [ReH 4( meso-P 4)] +. The T 1 values of the hydride resonances of the hydride complexes suggested that all are classical rhenium hydride complexes as the Re centres are too basic to form η 2-dihydrogen complexes. Re(H 2BEt 2)( rac-P 4) crystallized in the space group C2/ c with cell parameters a = 17.651(3), b = 13.874(2), c = 17.694(4) Å, β = 102.22(2)°, V = 4235(3) Å 3, Z = 4 R = 0.028 and R w = 0.029 for the 3343 reflections with I > 3σ( I). The BH 2Et 2 − unit is bound to rhenium via the two bridging hydrides.