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

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(1) reagents Tl(Bm(R)) (R = Me, Bu-t) or Tl(TMR) (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(Tmp-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 [NiP2S2H] cores and resemble a number of transient species that play a key role in the catalytic cycle of [NiFe] hydrogenases. (C) 2003 Elsevier Ltd. All rights reserved.