Synthesis and characterisation of 1,2-bis(dimethylphosphino)ethane (dmpe) complexes of chromium-(0) and -(IV): X-ray crystal structures of trans-Cr(N2)2(dmpe)2, cis-Cr(CO)2(dmpe)2, Cr(C2Ph2)2(dmpe), and CrH4(dmpe)2

Abstract

The reduction of trans-CrCl₂(dmpe)₂[dmpe = 1,2-bis(dimethylphosphino)ethane] in tetrahydrofuran by sodium amalgam under dinitrogen leads to the complex trans-Cr(N₂)₂(dmpe)₂, under carbon monoxide to the known cis-Cr(CO)₂(dmpe)₂, and in presence of Bu^tNC to trans-Cr(CNBu^t)₂(dmpe)₂. Interaction of trans-Cr(N₂)₂(dmpe)₂ with ethylene, buta-1,3-diene, diphenylacetylene, and hydrogen (under irradiation) gives, respectively, trans-Cr(C₂H₄)₂(dmpe)₂, cis-Cr(η⁴-C₄H₆)(dmpe)₂, Cr(PhCCPh)₂(dmpe), and CrH₄(dmpe)₂. Infrared and nuclear magnetic resonance spectra are reported together with X-ray crystal structures of four of the complexes. The trans-bis(dinitrogen) complex is centrosymmetric with octahedral geometry and Cr–N and Cr–P distances of 1.874(3) and 2.296(1)Å, respectively. The N–N bond length, 1.122(3)Å, is normal. The cis-dicarbonyl complex is also octahedral with a Cr–C distance of 1.812(6)Å; the Cr–P distances are different at 2.343(3)Åtrans to CO and 2.278(3)Åtrans to P, reflecting large differences in trans influence between CO and phosphine. The diphenylacetylene complex has π-bonded acetylene groups with Cr–C distances in the range 1.886(5)–l.980(5)Å and a chelating dmpe ligand, with Cr–P distances of 2.280(3), 2.298(3)Å. The chromium(IV) hydride has a dodecahedral structure with phosphines occupying the B sites [Cr–P 2.255(3)Å] and the hydrogen atoms the A sites [Cr–H 1.57(3)Å].