Abstract
Bonding characteristics of the H2-coordinating 16 valence electron species W(CO)3(PR3)2 (R = CHMe2, cyclohexyl (Cy)) were detd. by studying stable complexes with the poorly 2 electron-donating but strongly p-accepting cationic ligand N-methylpyrazinium (mpz+). In comparison with the related complex with W(CO)5, the 1H NMR and electrochem. data suggest a strong degree of p back-donation from W(CO)3(PR3)2 to the cationic acceptor in the ground state. This view is supported by the crystal structure anal. of (mpz)W(CO)3(PCy3)2(PF6) which reveals a trans,mer configuration with a short W-N bond (210.1(10) pm). Crystal data: monoclinic, space group P21/c, a 9.079(2), b 12.859(3), c 40.981(1) \AA, b 91.19(1)°, Z = 4, R = 0.067, Rw = 0.059. Redn. to the N-methylpyrazinium radical complexes yields highly resolved ESR spectra which show the loss of 1 phosphine ligand in the case of the tricarbonyl complexes. Even the W(CO)3(PR3) fragment induces considerable spin delocalization from the pyrazinium radical ligand to the metal. on SciFinder(R)
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