Carboalumination of a chromium–chromium quintuple bond

Abstract

Bonds are at the very heart of chemistry. Although the order of carbon–carbon bonds only extends to triple bonds, metal–metal bond orders of up to five are known for stable compounds, particularly between chromium atoms. Carbometallation and especially carboalumination reactions of carbon–carbon double and triple bonds are a well established synthetic protocol in organometallic chemistry and organic synthesis. We now extend these reactions to compounds containing chromium–chromium quintuple bonds. Analogous reactivity patterns indicate that such quintuple bonds are not as exotic as previously assumed. Yet the particularities of these reactions reflect the specific nature of the high metal–metal bond orders.

Cycloaddition Reactions of a Chromium–Chromium Quintuple Bond

“…Only very few reports on quintuple bond reactivity have appeared in the literature so far. [12] Quintuply bonded bimetallic complexes show a potential for small-molecule activation, particularly on a diatomic platform that can provide from two to eight (in principle even ten) electrons. These complexes feature not just low-valent metal centres, they are also coordinatively highly unsaturated.…”

Formation of cyclo‐E42− Units (E4=P4, As4, AsP3) by a Complex with a CrCr Quintuple Bond

“…[10] Until now only very few quintuple bond reactivity studies have appeared. [11] Activation of white phosphorus by main group elements [12] and transition metals [13] is an active research area in chemistry. However, bimetallic activation by transition metals is very rare.…”

Haloacylation of the Quintuple‐Bonded Group VI Metal Amidinate Dimers and Disproportionation of Acyl Groups to Form Carbynes

“…[7] These low-coordinate quintuple-bonded species not only have interesting metal-metal bonding, but also show remarkable reaction chemistry. [8][9][10][11][12][13][14][15][16] Recent studies have indicated that there are strong analogies between the d component of the metal-metal quintuple bonds and the p component of the carbon-carbon multiple bonds. For example, the quintuple bonded molybdenum amidinate dimers [Mo 2 {m-k 2 -RC(N-2,6-iPr 2 C 6 H 3 ) 2 } 2 ] (R = H (1), Ph) [17] react with two equivalents of terminal alkynes to give the first aromatics containing two multiple-bonded dimetal units by a [2+2+2] cycloaddition process, [14] while its chromium analogue [Cr 2 {m-k 2 -HC(N-2,6-iPr 2 C 6 H 3 ) 2 } 2 ] (2) [18] reacts with alkynes to afford [2+2] adducts.…”

“…[13] These reactivity analogies between p p and d d systems inspired us to explore functionalization of the metal-metal quintuple bonds.…”