The chemistry of the carbon-transition metal double and triple bond: Annual survey covering the year 2013

Chasing Multiple Bonding Interactions between Alkaline‐Earth Metals and Main‐Group Fragments

“…[90] Only three years later Mg II alkylidene [(Me 3 Si) 2 C{MgBr(thf) 2 } 2 ]( 1, Figure 2) was crystallographically authenticated, featuring Mg-C distances of 2.10(4) and 2.14(4) ,r espectively. [91] Treatment of 1 with 1,4-dioxane and hence manipulation of the Schlenke quilibrium did not afford the desired homoleptic [75,82] TheM g-C distances of 2.125(5) and 2.134 (5) in compound 2 are comparablet o those in the thf adduct 1 (vide supra). The SiMe 3 groups in 1 and 2 not only enhanced the solubility of the corresponding compounds, but more importantly,i mparted considerable stabilization of the carbdianion, both via steric shielding (kinetic stabilization) and partial delocalization of the negative charge (thermodynamic stabilization).…”

“…Transition-metal-carbenec omplexes [TM=CR 2 ]a re well established in av ariety of useful reactions such as olefin metathesis or olefination of carbonyl compounds. [2][3][4][5][6] Depending on the substitution pattern they are denoted electrophilicF ischertype carbenes (R = OR',N R ' 2 ), nucleophilic Schrock-type carbenes (R = alkyl;" alkylidenes"), and N-heterocyclicc arbenes. [60][61][62][63][64] While these compounds feature largely covalent bondingi nvolving the d-orbitalso ft he TM centers, [1] the respectivei nteractions in Ae complexes are predominantly electrostatic and unsurprisingly reports on [Ae=CR 2 ]s pecies remained scarce.…”

“…Compounds with multiple-bondingi nteractions betweena metal center and main-group fragments [1] feature ah ighly topical subjecto fc hemical research targeting organic/inorganic syntheses and catalytic transformations as key issues. [2][3][4][5][6] Being well-established for d-transition metals (even commercially applied) [7][8][9][10][11][12] and the 5f-element uranium, [13] derivatives of the 4f elements (lanthanides) emerged as av ibrant field only during the past 10 years. [14][15][16][17][18] Ar espective alkaline-earth (Ae) metal chemistry hasr emained underdeveloped.…”

Understanding the Mechanism of the Divergent Reactivity of Non-Heteroatom-Stabilized Chromium Carbene Complexes with Furfural Imines: Formation of Benzofurans and Azetines

“…Since their discovery in 1964, and especially during the last few decades, group 6 Fischer carbene complexes have demonstrated high versatility as a powerful synthetic tool. − However, non-heteroatom-stabilized carbene complexes, first reported by Casey in 1973, did not emerge as an alternative reagent until recently due to their low stability. Among them, non-heteroatom-stabilized alkynylcarbenes, smoothly in situ synthesized from the corresponding Fischer-type alkoxycarbenes, resulted in synthetically useful and experienced significant differences in terms of reactivity with their alkoxycarbene analogues.…”

Rare-earth metal methylidene complexes with Ln3(μ3-CH2)(μ3-Me)(μ2-Me)3core structure

“…Multiple metal-carbon bonds, predominantly alkylidene units "MvCR 2 ", continue to trigger immense research activities in organometallic synthesis and catalysis. [1][2][3][4][5][6][7][8] Schrock's neopentylidene complex (tBuCH 2 ) 3 Ta(vCHtBu) 9,10 marked the first example of a stable transition metal alkylidene complex, with the bulky tBu substituents at the α-carbon atom impeding intermolecular decomposition pathways. In contrast, methylidene "CH 2 2− " species are sterically less protected against bimolecular reactions, and hence present a particular challenge and are found to be kinetically labile.…”