Poly(mercaptoimidazolyl)borate chemistry and the predominance of κ3-S,S,H over κ2-S,S or κ3-S,S,S coordination modes: unexpected formation of square pyramidal Ni(II) complexes

Abstract The paramagnetic nickel(II) complexes [(dppe)Ni(L)]X (L=Bm R or Tm R ) have been readily prepared from the appropriate 1,2-bis(diphenylphosphino)ethane adducts Ni(dppe)X 2 (X=Cl, Br) and the thallium(I) reagents Tl(Bm R ) (R=Me, Bu t ) or Tl(Tm R ) (R=Me, Bu t , p-Tol), and isolated as carmine to deep purple solids in 75–95% yield. X-ray diffraction studies of [(dppe)Ni(Bm Me )]Cl and [(dppe)Ni(Tm p -Tol )]Cl revealed the presence of a weak pseudo-axial Ni⋯H–B interaction and an overall square pyramidal geometry in each complex. As such, the cationic complexes [(dppe)Ni(L)] + are the first structurally characterized species having [NiP 2 S 2 H] cores and resemble a number of transient species that play a key role in the catalytic cycle of [NiFe] hydrogenases.