Octahedral Alkynylphosphine Ruthenium(II) Complexes: Synthesis, Structure, and Electrochemistry

Reaction of [RuCl2(PPh3)3] with
excess of PPh2CCFc (Fc = ferrocenyl) proceeds with
formation of [trans-RuCl2(PPh2CCFc)4] (3), which reacts with HCCR
(R = Ph, Tol) via dissociative loss of one PPh2CCFc
ligand to yield vinylidene complexes [mer,cis-RuCl2(CCHR)(PPh2CCFc)3] (R = Ph 4a, Tol 4b). Reported
herein also is the preparation of a series of trans/cis bis(alkynyl)tetrakis(alkynylphosphine) derivatives
[Ru(CCR′)2(PPh2CCR)4] (R′ = Ph, Tol; R = Ph, trans/cis-5a, 5b; R = Tol, trans/cis-6a, 6b; R = Fc, trans/cis-7a, 7b), synthesized by reaction of [trans-RuCl2(PPh2CCR)4] (R = Ph 1,
Tol 2, Fc 3) with an excess of HCCR′
(R′ = Ph, Tol) and NEt3, in the presence or absence
of NaPF6. In the preparation of cis-5a, the ketovinyl derivative [mer-Ru{κC,O-C(CH2COCH3)CHPh}Cl(PPh2CCPh)3] (8) was obtained as
a byproduct in the presence of acetone. The solid-state structures
of complexes 3, trans-5a, trans-7a, and 8 have
been determined by X-ray diffraction studies, showing the presence
of several types of weak intramolecular hydrogen interactions. The
cyclic voltammetry data for the mononuclear complexes (1, 2, trans/cis-5/6, and 8) show a quasi
reversible oxidation attributed to the RuII/III couple
and reveal a marked influence of the ligands and the geometry on the E1/2 values. The electrochemical behavior of
the ferrocenylethynyldiphenylphosphine compounds 3, 4, and trans/cis-7 is more complex. Spectroelectrochemical comparative
studies of related complexes (trans-7b vs trans-5b; 4 vs [RuCl2(CCHTol)(PPh2CCPh)3])
suggest that the first oxidation occurs at the ferrocene site of the
PPh2CCFc ligand.