Alkyl, Silyl, and Phosphane Ligands—Classical Ligands in Nonclassical Bonding Modes

Abstract

Alkyl, silyl, and phosphane ligands are amongst the most familiar and ubiquitous ligands in organometallic and coordination chemistry. The C, Si, and P donor atoms of these ligands are sp3‐hybridized and the ligands are related to each other by the isolobal analogy: (CR3)−(SiR3)−PR3. Herein, we demonstrate that although a number of unusual observations concerning the reactivity and bonding of these ligands appears unrelated at first sight, they in fact provide offer an exiting and consistent picture that may form the basis for new paradigms. The characterization of stable complexes in which alkyl, silyl, and phosphane ligands behave as symmetrical bridges confirms that there is no inherent thermodynamic instability associated with these bonding situations, and, in fact, reactivity studies suggest that these ligands should be able to bridge between metal centers in reaction intermediates or transition states.

An organometallic tetranuclear cluster with phosphine and phosphido ligands in nonclassical bonding modes: X-ray structural characterization

“…The Pd(2)-C(37) distance (2.391(5) Å ) is rather short [18][19][20][21][22][23][24][25], as is the Pd(2)-P(2) distance (2.272(1) Å ), in fact it is even Scheme 1. shorter than the Pd(1)-P(2) and Pt(1)-P(2) distances (2.389(1) and 2.358(1) Å , respectively). These data indicate that the P(2)-C(37) bond interacts with the Pd(2) centre giving rise to a 2e-3c bond or an agostic-like interaction of a P-C sp2 bond with an unsaturated metal atom, as it has been recently called for related phosphine complexes [26][27][28].…”

Functional ligands and complexes for new structures, homogeneous catalysts and nanomaterials

“…is by definition not possible with mononuclear systems. This innovation may be illustrated by the discovery of the bridging behaviour of alkoxysilyl ligands which opens considerable perspectives not only in molecular synthetic chemistry but also in homogeneous catalysis and material sciences [77], and by the recently delivered proof that the ubiquitous phosphine [79] and silyl ligands [80], which are related by the isolobal analogy [81], can also behave as bridging ligands, a situation that was predicted back in 1989 in the former case [82]. The potential of cluster complexes to mediate unique bond forming/breaking reactions [83] or of heterobimetallic complexes to display reactivity patterns that are unknown for their homometallic analogs, as recently observed in the dimerization of methylacrylate promoted by a Ni-Mo complex [84] is also noteworthy.…”

Methyl Complexes of the Transition Metals

“…This section will deal with homo-and some hetero-dimetallic complexes of transition metals with bridging methyl ligands. Some excellent reviews and book chapters have focused on this topic, 143 some considering the metal-metal bonding of the bridging methyl compounds and the nature of the bridging ligands as threecentre two-electron bonds. 9,144 A search in the Cambridge Structural Database for bimetallic transition metal complexes with bridging methyl ligands produced only 75 results, a very small number compared to the more than five thousand entries retrieved for metal methyl (TM-CH3) compounds.…”

“…Bridging modes for a methyl ligand in bimetallic complexes (ref. 143) Bridging modes for a methyl ligand in bimetallic complexes are represented in Scheme 28 (modified from reference 143). Mode I is common among di-zirconium species ( Figure 5).…”