Covalent Uranium Carbene Chemistry

Abstract

After seminal reports of covalent uranium carbene U=C complexes in the 1980s by Gilje, the area fell dormant for around 30 years. However, in the past five years, there has been a resurgence of interest in the area. Despite recent advances, the classification of these U=C complexes as either methanediides, carbenes, or alkylidenes has remained a contentious issue. Herein, we review U=C complexes reported to date, along with reactivity and computational studies, and conclude that although U=C complexes sit midway on the continuum between rare-earth methanediides and Schrock-type alkylidenes, they can be justifiably described as carbenes.

Double dative bond between divalent carbon(0) and uranium

“…The short U−C bond in complex 2 prompted us to appraise uranium−carbon multiple bond chemistry 44–46 . The first uranium carbene was reported in 1981, and was stabilized by a phosphorus substituent 29 .…”

Uranium–Carbene–Imido Metalla‐Allenes: Ancillary‐Ligand‐Controlled cis‐/trans‐Isomerisation and Assessment of trans Influence in the R2C=UIV=NR′ Unit (R=Ph2PNSiMe3; R′=CPh3)

“…The U IV =N (1.977 (4) ) and U IV =C( 2.491(6) ) bond lengths are similar to other terminal U IV =Nb ond lengths( 1.95-2.04 ) [16c, 17] or U IV = C carbene bond lengths (2.30-2.50 ). [18] For the latter,c are should be taken when judging the nature of the interaction only by bond length, but multiple bond characteri sc orroborated by computational analysis (see below). Multiple bond character of the U IV =Nl inkagei sa lso suggested by the linear U=N imido ÀCR 3 arrangement (173.9(4)8).…”

“…Multiple bond character of the U IV =Nl inkagei sa lso suggested by the linear U=N imido ÀCR 3 arrangement (173.9(4)8). The most intriguing feature of 2 is the cis-C=U IV =Nu nit, with aC carbene =U=N imido angle of 111.28 (18)8. This is in sharp contrast to the overwhelmingly prevalent trans-E=U=E' moieties, in which aE=U=E' is around1 808.T he BIPY bond lengths are consistentw ith its neutralf orm, and the UÀN BIPY bond lengths are long (2.669(4) and2 .693 (5) ), and thus dative.…”

“…Selected bond lengths []: U1ÀC1 2.500(6), U1ÀN3 2.032(5), U1ÀN1 2.507(4), U1À N2 2.567(4), U1ÀN4 2.586(5), U1ÀN5 2.580 (5). Selectedbondangles [8]: C1-U1-N31 75.97 (18),U 1-N3-C2 171.6(4). Chem.…”

Thorium(IV) alkyl synthesis from a thorium(III) cyclopentadienyl complex and an N-heterocyclic olefin

“…Compared to extensive investigations spanning decades regarding transition metal carbene complexes, related studies in the actinide series remain relatively rare [1][2][3][4][5][6]. After Gilje's seminal report of the tris(cyclopentadienyl) uranium-carbene complex, [U(η 5 -Cp) 3 (CHPMe 2 Ph)] (I, Figure 1) [7], and some related reactivity studies [8][9][10][11][12][13][14][15][16], the area fell into abeyance for over 25 years.…”