Synthesis and Characterization of Platinum and Palladium Complexes Featuring a Rare Secondary Borane Pincer Motif
journal contribution
posted on 2018-06-26, 19:51 authored by Angelo Iannetelli, Graham Tizzard, Simon J. Coles, Gareth R. OwenThe synthesis and characterization
of a series of platinum and
palladium complexes containing a secondary borane Z-class ligand supported
by 2-mercaptopyridine heterocycles is reported herein. Addition of
2 equiv of Na[H2B(mp)2] to [Pt(μ-Cl)(COEOMe)]2 (where COEOMe = 8-methoxycyclooct-4-en-1-ide)
in the presence of 2 equiv of a tertiary phosphine (PR3 = PPh3, PCy3, PCyp3, P(o-tol)3, PPh2(o-tol),
PPh2(2-(3-methyl)indolyl)) leads to the formation of the
complexes [Pt{κ3-S,B,S-HB(mp)2}(PR3)] (1–6).
Addition of 2 equiv of Na[H2B(mp)2] to [Pd(μ-Cl)(COEOMe)]2 in the presence of 2 equiv of a tertiary
phosphine (PR3 = PPh3, PCy3, PCyp3, PPh2(o-tol)) leads to the formation
of the complexes [Pd{κ3-S,B,S-HB(mp)2}(PR3)] (7–10).
It was also demonstrated that the synthesis of the palladium complex 7 could be achieved from the palladium precursor [PdCl(Me)(COD)]
(where COD = 1,5-cyclooctadiene) as an alternative synthetic strategy.
In the above reactions, either the COEOMe fragment or the
methyl fragment serves to act as a “hydride acceptor”
facilitating the ultimate transformation of the borohydride-based
ligand [H2B(mp)2]− to the
corresponding secondary borane κ3-S,B,S coordinated HB(mp)2 pincer ligand. The complexes [Pd{κ3-S,B,S-HB(mp)2}(PR3)] and [Pt{κ3-S,B,S-HB(mp)2}(PR3)] are rare examples of metal–borane
complexes where one hydrogen substituent remains at the boron center.
These compounds have particularly short palladium– and platinum–boron
distances, the shortest of the structurally characterized compounds
being 2.067(6) Å for [Pd{κ3-S,B,S-HB(mp)2}(PPh2(o-tol))] and
2.076(10) Å for [Pt{κ3-S,B,S-HB(mp)2}(PCy3)], respectively (the shorter
distances of two independent complexes in the unit cells of both structures).
