Metal-only Lewis Pairs of Rhodium with s, p and d-Block Metals.

Sonia Bajo,María M Alcaide,Macarena G Alférez,Joaquín López-Serrano,Jesús Campos

doi:10.1002/chem.202003167

Abstract

Metal‐only Lewis pairs (MOLPs) in which the two metal fragments are solely connected by a dative M→M bond represent privileged architectures to acquire fundamental understanding of bimetallic bonding. This has important implications in many catalytic processes or supramolecular systems that rely on synergistic effects between two metals. However, a systematic experimental/computational approach on a well‐defined class of compounds is lacking. Here we report a family of MOLPs constructed around the RhI precursor [(η 5‐C5Me5)Rh(PMe3)2] (1) with a series of s, p and d‐block metals, mostly from the main group elements, and investigate their bonding by computational means. Among the new MOLPs, we have structurally characterized those formed by dative bonding between 1 and MgMeBr, AlMe3, GeCl2, SnCl2, ZnMe2 and Zn(C6F5)2, as well as spectroscopically identified the ones resulting from coordination to MBArF (M=Na, Li; BArF −=[B(C6H2‐3,5‐(CF3)2)4]−) and CuCl. Some of these compounds represent unique examples of bimetallic structures, such as the first unambiguous cases of Rh→Mg dative bonding or base‐free rhodium bound germylene and stannylene species. Multinuclear NMR spectroscopy, including 103Rh NMR, is used to probe the formation of Rh→M bonds. A comprehensive theoretical analysis of those provides clear trends. As anticipated, greater bond covalency is found for the more electronegative acids, whereas ionic character dominates for the least electronegative nuclei, though some degree of electron sharing is identified in all cases.

Highlights

The unambiguous recognition of MÀM bonding within the determination of the Mn2(CO)10 structure[1] was a landmark discovery in transition metal chemistry and set the grounds for exciting developments in the field of polynuclear molecular compounds.[2]
The growing interest on Metal-only Lewis pairs (MOLPs) is reflected by increased number of studies focusing either on accessing new structures or computationally investigating families of compounds already prepared, whereas a combined effort on a series of MOLPs is still lacking
We provide here a comprehensive computational investigation on the RhÀM bonding of the prepared Rh MOLPs, with several sound correlations found for relevant parameters associated to the metalto-metal bond

Summary

Introduction

The unambiguous recognition of MÀM bonding within the determination of the Mn2(CO) structure[1] was a landmark discovery in transition metal chemistry and set the grounds for exciting developments in the field of polynuclear molecular compounds.[2] Only a few years later, the existence of multiple bonding between metals was demonstrated by Cotton and coworkers in [Re2Cl8],[2,3] shattering at the same time the common belief of a maximum bond order of three, as seen in the p-block. Chemistry - A European Journal published by WileyVCH GmbH.

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