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

Abstract

Reduction (Na–Hg, tetrahydrofuran) of trans-[RuCl₂(CNBu^t)₄] in the presence of excess of CNBu^t gives [Ru(CNBu^t)₅], which on reaction with PPh₃ affords [Ru(CNBu^t)₄(PPh₃)]. The latter is also formed on reduction of trans-[RuCl₂(CNBu^t)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 CNBu^t[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 CNBu^t, CNPrⁱ, CNEt, or CNC₆H₃Me₂-2,6 affords the crystalline complexes [Fe(CNR)₅](R = Bu^t, Prⁱ, Et, or C₆H₃Me₂-2,6). A single-crystal X-ray diffraction study of [Fe(CNBu^t)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(CNBu^t)₅] with PPh₃(1 mol) gives [Fe(CNBu^t)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 CNBu^t gives [Os(CNBu^t)₃(1,5-C₈H₁₂)]. The structure in solution and dynamic behaviour of these complexes is discussed.