T‐Shaped Platinum(II) Complexes Stabilised by Bulky N‐Heterocyclic Carbene Ligands

Abstract

Pt to a T! Treating bulky N‐heterocyclic carbene (NHC) ligands with [PtMe3I]4 results in rapid elimination of ethene and formation of [PtMeI(NHC)2] complexes. These complexes are suitable materials for the synthesis of T‐shaped platinum(II) complexes stabilised by agostic interactions. X‐ray structure determination of one of these complexes shows a rather long ζ agostic interaction (see figure).

True and masked three-coordinate T-shaped platinum(II) intermediates

“…This is one of the rare neutral T-shaped Pt(II) complexes. Referring to NHC ligands, Rivada-Wheelaghan et al isolated the three-coordinate methyl [Pt(Me)(IPr) 2 ] + ( A10 ) and cyclometalated [Pt(NHC’)NHC] + complexes (NHC = IPr A11a , I t -Bu (1,3-bis( tert -butyl)imidazol-2-ylidene) A11b ; NHC’ = cyclometalated ligand) [44]. In sharp contrast with the analogous T5 and T6 (Fig.…”

“…The 1 J Pt,C is also very large for these methyl derivatives, ranging from 755 to 780 Hz (Table 2). Cyclometalated phosphine [39–40] and NHC [28,44] Pt(II) compounds were also shown to have very large 2 J Pt,H coupling constants (slightly larger than those for the non-cyclometalated versions) spanning from 107 Hz to ca. 135 Hz (average) and 1 J Pt,C values between 805 and 975 Hz.…”

“…Although the number of species that have been authenticated by crystallographic or spectroscopic methods is still very limited, the best and most general method for obtaining them is by removing a halogen ligand (Cl, Br, I) from the platinum coordination center in 1 by using a halogen abstractor with a poor coordinating anion, such as tetrakis[3,5-(trifluoromethyl)phenyl]borate or hexafluoroantimonate (Scheme 1) [19–21 28,39,44]. …”

“…15 and arises from the rapid intramolecular exchange of the C–H bond involved in the agostic interaction. In several cases, such as A11a [44], the overlapping of the proton signals and signal averaging of the ligands avoid drawing a conclusion about the nature of the agostic interaction at work in solution. Recently, ab initio molecular dynamics (AIMD) simulations of some representative T-shaped Pt(II) complexes ( T5b , A2b and A11a ), performed in explicit dichloromethane solvent, have provided a detailed description of the mechanism by which the equivalence of signals takes place [106].…”

Computational insights on the possibility of tri-coordinated cisplatinated adducts with protein models

“…Today, a general consensus exists in which these species are considered unstable and only transitory in nature. Nonetheless, tri-coordinated Pt(II) organometallic complexes have been increasingly reported in the recent years [16][17][18][19][20][21][22]. Most of them adopt a T-shaped geometry that is stabilized by a weak agostic interaction between one of the ligand and the vacant site of the metal.…”