Coordination of a Hemilabile Pincer Ligand with an Olefinic Backbone to Mid-to-Late Transition Metals

The
coordination chemistry of a neutral tPCHCHP
pincer (tPCHCHP = 2,2′-bis­(di-iso-propyl­phosphino)-trans-stilbene)
with metals that form stable complexes in the +1 oxidation state was
studied and (tPCHCHP)­CoCl, (tPCHCHP)­CoCl­(CO), (tPCHCHP)­RhCl,
(tPCHCHP)­Cu­(OTf), [(tPCHCHP)­Cu]­[PF6], and [(tPCHCHP)­Ag]­[PF6] were synthesized and characterized.
In order to determine whether the coordination mode is dependent on
the oxidation state of the metal, some +2 metal complexes, (tPCHCHP)­CoCl2 and (tPCHCHP)­FeBr2, were also investigated. The coordination
of the olefinic backbone is not observed in (tPCHCHP)­FeBr2, (tPCHCHP)­CoCl2, (tPCHCHP)­Cu­(OTf), or [(tPCHCHP)­Ag]­[PF6], but η2-coordination is present in [(tPCHCHP)­CoCl]­[BArF4], [(tPCHCHP)­FeBr]­[BArF4], (tPCHCHP)­CoCl,
(tPCHCHP)­CoCl­(CO), (tPCHCHP)­RhCl, and [(tPCHCHP)­Cu]­[PF6]. Cobalt­(II), iron­(II), and copper­(I) formed complexes with
the ligand in both coordination modes. All metal complexes were characterized
by multinuclei NMR spectroscopy, X-ray crystallography, and elemental
analysis.