Chemistry of low-valent metal isocyanide complexes. Part 1. Synthesis of zerovalent iron and ruthenium complexes. Crystal and molecular structures of tetrakis(t-butyl isocyanide)(triphenylphosphine)ruthenium and pentakis(t-butyl isocyanide)iron

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Abstract
Reduction (Na–Hg, tetrahydrofuran) of trans-[RuCl2(CNBut)4] in the presence of excess of CNBut gives [Ru(CNBut)5], which on reaction with PPh3 affords [Ru(CNBut)4(PPh3)]. The latter is also formed on reduction of trans-[RuCl2(CNBut)4] with sodium amalgam in the presence of 1 mol equivalent of PPh3. In order to establish the structural identity of this complex a single-crystal X-ray diffraction study has been made. Crystals of the complex are monoclinic, space group P21/c, Z= 4, in a unit cell of dimensions a= 12.174(4), b= 29.193(13), c= 11.454(3)Å, and β= 102.62(2)°. The structure has been refined to R 0.094 (R′ 0.089) for 1 763 reflections. The complex has a trigonal-bipyramidal structure with PPh3 and two bent CNBut[mean C–N–C 130(2)°] ligands occupying equatorial sites, and two essentially linear isocyanides in the axial sites. A similar reduction of FeBr2 in the presence of excess of CNBut, CNPri, CNEt, or CNC6H3Me2-2,6 affords the crystalline complexes [Fe(CNR)5](R = But, Pri, Et, or C6H3Me2-2,6). A single-crystal X-ray diffraction study of [Fe(CNBut)5] has been undertaken. Crystals of the complex are monoclinic, space group P21/n,Z= 8, in a unit cell of dimensions a= 18.930(8), b= 11.529(3), c= 28.968(8)Å, and β= 108.63(1)°. The structure has been refined to R 0.099 (R′ 0.129) for 4 339 reflections. There are two crystallographically independent molecules in an asymmetric unit, each of which shows marked deviation from idealised trigonal-bipyramidal geometry, the radial ligands being bent. Reaction of [Fe(CNBut)5] with PPh3(1 mol) gives [Fe(CNBut)4(PPh3)], and treatment of [Fe(CNEt)5] with CNC6H3Me2-2,6 affords [Fe(CNEt)3(CNC6H3Me2-2,6)2]. Reduction of [{OsCl2(1,5-C8H12)}n] with potassium amalgam in the presence of excess of CNBut gives [Os(CNBut)3(1,5-C8H12)]. The structure in solution and dynamic behaviour of these complexes is discussed.