Synthesis and crystal structures of nickel(ii) and palladium(ii) complexes with o-carboranyl amidine ligands

Abstract

A number of new nido-carboranyl amidines 10-R(CH₂)_nNHC(Et)HN-7,8-C₂B₉H₁₁ (n = 2, R = OH, OMe, and NMe₂; n = 3, R = OH) were synthesized by the nucleophilic addition of amino alcohols and N,N-dimethylethylenediamine to the highly activated –CN⁺– triple bond of the 10-propionitrilium derivative of nido-carborane. A similar reaction of 10-EtCN-7,8-C₂B₉H₁₁ with ethylenediamine unexpectedly resulted in the cleavage of the CN bond to form the ammonium derivative 10-H₃N-7,8-C₂B₉H₁₁. The complexation of the synthesized carboranyl amidines 10-MeO(CH₂)₂NHC(Et)HN-7,8-C₂B₉H₁₁ and 10-Me₂N(CH₂)₂NHC(Et)HN-7,8-C₂B₉H₁₁ with nickel and palladium phosphine complexes [(Ph₃P)₂MCl₂] (M = Ni, Pd) was studied. The reactions with 10-MeO(CH₂)₂NHC(Et)HN-7,8-C₂B₉H₁₁ result in half-sandwiched metallacarborane complexes with the retention of one triphenylphosphine ligand [3-Ph₃P-3-(8-MeOCH₂CH₂NC(Et)NH)-3,1,2-MC₂B₉H₁₀], while the reactions with 10-Me₂N(CH₂)₂NHC(Et)HN-7,8-C₂B₉H₁₁ proceed with the complete loss of the phosphine ligands and lead to the formation of complexes with the η⁵:κ²(N,N′)-coordinated carboranyl amidine ligand [3,3-(8-Me₂NCH₂CH₂NC(Et)NH)-3,1,2-MC₂B₉H₁₀]. The crystal molecular structures of the synthesized complexes were determined by single crystal X-ray diffraction.