Reactions of Late First-Row Transition Metal (Fe-Zn) Dichlorides with a PGeP Pincer Germylene

The reactivity of the PGeP germylene 2,2'-bis(di-isopropylphosphanylmethyl)-5,5'-dimethyldipyrromethane-1,1'-diylgermanium(II), Ge(pyrmPiPr₂ )₂ CMe₂ , with late first-row transition metal (Fe-Zn) dichlorides has been investigated. All reactions led to PGeP pincer chloridogermyl complexes. The reactions with FeCl₂ and CoCl₂ afforded paramagnetic square planar complexes of formula [MCl{κ³ P,Ge,P-GeCl(pyrmPiPr₂ )₂ CMe₂ }] (M=Fe, Co). While the iron complex maintained an intermediate spin state (S¹ ; μ_eff =3.0 μ_B ) over the temperature range 50-380 K, the effective magnetic moment of the cobalt complex varied linearly with temperature from 1.9 μ_B at 10 K to 3.6 μ_B at 380 K, indicating a spin crossover behavior that involves S^1/2 (predominant at T<180 K) and S^3/2 (predominant at T>200 K) species. Both cobalt(II) species were detected by electron paramagnetic resonance at T<20 K. The reaction of Ge(pyrmPiPr₂ )₂ CMe₂ with [NiCl₂ (dme)] (dme=dimethoxyethane) gave a square planar nickel(II) complex, [NiCl{κ³ P,Ge,P-GeCl(pyrmPiPr₂ )₂ CMe₂ }], whereas the reaction with CuCl₂ involved a redox process that rendered a mixture of the germanium(IV) compound GeCl₂ (pyrmPiPr₂ )₂ CMe₂ and a binuclear copper(I) complex, [Cu₂ {μ-κ³ P,Ge,P-GeCl(pyrmPiPr₂ )₂ CMe₂ }₂ ], whose metal atoms are in tetrahedral environments. The reaction of the germylene with ZnCl₂ led to the tetrahedral derivative [ZnCl{κ³ P,Ge,P-GeCl(pyrmPiPr₂ )₂ CMe₂ }].