A unique hydrido phosphine-borane iron(II) complex [(dppa)(Ph₂P-N-P(BH₃)Ph₂)Fe(H)] (1) was obtained by the reaction of iron(II) chloride and two equivalents of bis(diphenylphosphino)amine (dppa) with an excess of sodium borohydride in acetonitrile-ethanol mixtures. Detailed investigations of the reaction revealed that a mixture of cis- and trans-[(dppa)₂Fe(NCMe)₂]²⁺ is formed prior to the reduction by sodium borohydride. Depending on the solvent, different products were obtained by the reduction: in acetonitrile-ethanol mixtures the hydrido phosphine-borane complex 1 is formed by formal insertion of BH₃, while the reduction in pure acetonitrile results in the formation of the cationic complex trans-[(dppa)₂Fe(H)(NCMe)](BH₄) (4). Complex 4 is remarkably stable in ethanol and does not undergo phosphine-borane formation, even in the presence of excess sodium borohydride. This observation suggests that the phosphine-borane complex is generated by the reaction with the first equivalent of sodium borohydride with the participation of ethanol, followed by deprotonation or dihydrogen elimination. Experiments with similar diphosphine ligands, such as bis(diphenylphosphino)methane, did not yield a phosphine-borane complex, indicating the crucial role of the amine group in the observed reactivity.
The reaction of sym‐dimethyltetraphenyl carbodiphosphorane (CDPMe) with [Ni(CO)4] under standard conditions yields the CDPMe‐ and carbon monoxide‐bridged dinickel pentacarbonyl complex [Ni2(CO)4(µ2‐CO)(µ2‐CDPMe)] (2). However, under an atmosphere of CO(g), reaction of [Ni(CO)4] with CDPMe gives the primal target complex [CDPMe‐Ni(CO)3] (3). The complexes were examined in solution (ESI‐MS, NMR) and in the solid state (IR, X‐ray diffraction analysis). The resulting Tolman electronic parameter (TEP) and percentage buried volume value (%Vbur) of CDPMe are presented and compared with hexaphenyl carbodiphosphorane (CDPPh). DFT calculations were performed to analyze the bonding situation in complexes 2 and 3.
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