Some rhenium hydride complexes with tetradentate phosphine co-ligands: the crystal structure of Re(H2BEt2)(racemic-tetraphos)

Article abstract of DOI:10.1016/0022-328X(93)83286-5

ReH5(PMePh2)3 reacts with P(CH2CH2PPh2)3 (PP3) in the absence of solvent at 180 deg C to give ReH(PMePh2)(PP3).Under similar conditions, ReCl3(PMePh2)3 reacts with tetraphosphine ligands PP3 or commercially available P4 (Ph2PCH2CH2P(Ph)CH2CH2P(Ph)CH2CH2PPh2) to produce ReCl3(PP3) and ReCl3(P4), respectively.Treatment of ReCl3(PP3) with NaBH4 yielded ReH3(PP3), which is converted into ⁺ when protonated.Treatment of ReCl3(P4) with NaBH4 in MeOH/benzene produced a mixture of ReH3(meso-P4) and ReH3(rac-P4).On the other hand, a mixture of ReH3(meso-P4) and the novel complex Re(BH2Et2)(rac-P4) was obtained when ReCl3(P4) was treated with an old sample of LiBHEt3 (actually containing LiBEt4/LiBH2Et2) in THF.Protonation of ReH3(meso-P4) produced ⁺.The T₁ 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 η²-dihydrogen complexes.Re(H2BEt2)(rac-P4) crysallized in the space group C2/c with cell parameters a=17.651(3), b=13.874(2), c=17.694(4) Angstroem, β=102.22(2)^o, V=4235(3) Angstroem³, Z=4, R=0.028 and R_w=0.029 for the 3343 reflections with I > 3?(I).The BH2Et^-2 unit is bound to rhenium via the two bridging hydrides.