A Bimetallic, Coordinated-Ketene Complex Formed from a Bimetallic Lithium–Carbon Spirocycle by Lithium-Mediated Insertion of CO into a Rhodium–Carbon Bond

✍ Scribed by Min Fang; Nathan D. Jones; Robert Lukowski; Jim Tjathas; Michael J. Ferguson; Ronald G. Cavell

• Publisher: John Wiley and Sons
• Year: 2006
• Tongue: English
• Weight: 159 KB
• Volume: 45
• Category: Article
• ISSN: 0044-8249
• DOI: 10.1002/anie.200503814

✦ Synopsis

Bimetallic complexes play a large role in organometallic chemistry in part because of the potential for cooperative catalytic applications. Of particular interest in this context are hetero-bimetallic systems constructed around a single-carbon (methylene) bridge (sometimes also classified as a "bridging carbene"). Most hetero-bimetallic systems are either "Aframe" complexes that are bridged by bis(phosphine) ligands or compounds containing a direct MÀM bond. [1] The use of lithium reagents as organic and organometallic synthetic precursors [2][3][4][5] is also relevant to the system described herein, and the importance of such reagents has warranted extensive interest from synthetic, structural, and theoretical perspectives. [6] There are, however, few structurally characterized lithium systems which contain a carbonbridged Li-C-precious-metal assembly, and only three of these cases involve Rh. [7,8] None of these bridged-carbene Rh complexes carries a phosphorus substituent on the central carbon atom.

A final facet of the system described herein is the insertion of CO into a metal-carbon bond, which is an important organometallic transformation. [9] In particular, metal ketene complexes (which can formally be considered as the derivatives of such insertion processes) are considered to play important roles in industrial Fischer-Tropsch syntheses [1e, 10] as well as in CO 2 fixation and functionalization, [11] and may be intermediates in the thermal and photochemical reactions of carbene/CO complexes. [12] In most cases, the existence of the intermediate ketene complex is only inferred because the general instability of such complexes hampers direct observation. Nevertheless, over the years, a number of ketene complexes has been prepared and structurally characterized. The varied chemistry of ketene complexes has been reviewed; [10f] it was noted that up to nine coordination modes