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Addition of Nitrogen-Containing Heteroallenes to Iron(II)-Hydrides

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journal contribution
posted on 12.07.2001 by Leslie D. Field, Warren J. Shaw, Peter Turner
The reactions between cis-Fe(dmpe)2H2 (dmpe = Me2PCH2CH2PMe2) (1) or cis-Fe(PP3)H2 (PP3 = P(CH2CH2PMe2)3) (2) and phenyl isothiocyanate (PhNCS), ethyl isothiocyanate (EtNCS), and phenyl isocyanate (PhNCO) were investigated. PhNCS reacts with 1 to form a variety of insertion products at low temperature, and the thermodynamic product hydridoiron N-phenylthioformimidate trans-Fe(dmpe)2(SCHNPh)H (3a) at 300 K. Addition of an excess of PhNCS to 1 produces the bis(insertion) product trans-Fe(dmpe)2(SCHNPh)2 (3c). EtNCS inserts into the iron−hydride bond of 1 to form a mixture of trans-Fe(dmpe)2(SCHNEt)H (4a, thermodynamic product) and cis-Fe(dmpe)2(SCHNEt)H (4b, kinetic product). Addition of an excess of EtNCS does not result in a second insertion but rather attack at the thioformimidato ligand to form trans-Fe(dmpe)2(SCHN+(Et)C(S)N-Et)H (4c). PhNCO reacts rapidly with 1 to form trans-Fe(dmpe)2(OCHNPh)H (5a) and higher oligomeric products. The addition of PhNCS, EtNCS, and PhNCO to 2 permits the formation of thermally stable, geometrically constrained cis products cis-Fe(PP3)(SCHNPh)H (6a), cis-Fe(PP3)(SCHNEt)H (7a), and cis-Fe(PP3)(OCHNPh)H (8a) in clean reactions. The hydridoiron N-phenylthioformimidate 6a reacts with a second equivalent of PhNCS to form cis-Fe(PP3)(SCHNPh)2 (6c), but oligomerization of EtNCS or PhNCO does not occur. All complexes have been characterized by multinuclear NMR andIR spectroscopy and mass spectrometry (electrospray), with elemental analysis or high resolution mass spectrometry confirming the structures of thermally stable complexes where possible. Complexes 3c and 4c were characterized by single-crystal X-ray crystallography.

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