Cr(i)Cl as well as Cr⁺are stabilised between two cyclic alkyl amino carbenes

Abstract

Complexes with two and three coordinate chromium(i).

What Wanzlick Did Not Dare To Dream: Cyclic (Alkyl)(amino)carbenes (cAACs) as New Key Players in Transition‐Metal Chemistry

“…Since the first syntheses of a homoleptic cationic bis‐cAAC‐coordinated gold(I) complex in 2008 and of a homoleptic neutral bis‐cAAC‐stabilized zinc(0) compound in 2013, a considerable number of stable [M(cAAC) 2 ] n + species of Group 6 to Group 12 metals (M; 17 – 25 ) and even two examples of stable homoleptic dinuclear complexes – [Co 2 (cAAC) 2 ] ( 26 )[45e] and [Au 2 (cAAC) 2 ] ( 27 ) – have been reported, mainly by the groups of Bertrand[45a], , and Roesky. [45b], [45d], [45e], , , [50a]…”

“…With exception of the palladium(0)[50a] and platinum(0)[50b] representatives, these compounds have been obtained by the same synthetic strategy (Scheme ): namely, bis‐adduct formation between cAAC and the appropriate metal halide, either (Scheme , A) MX 2 [for M = Cr ( 17 ), Mn ( 18 ), Fe ( 19 ), Co ( 20 ), Zn ( 21 )] or (Scheme , B) MX [for M = Cu ( 22 ), Au ( 23 )] in a first step and a subsequent transformation of these products into the desired low‐valent [M(cAAC) 2 ] complexes with a suitable reducing agent. In some cases homoleptic compounds [M(cAAC) 2 ] + with the metal in non‐zero oxidation state were also obtained as final products [M = Cr ( 17 )] or intermediates (M = Fe, Co, Cu, Au) through partial reduction and halide abstraction. It is of note that the reduction of mono‐cAAC adducts [CoCl 2 (cAAC)] and [AuCl(cAAC)] led to dimerization and formation of the dinuclear complexes [Co 2 (cAAC) 2 ] ( 26 )[45e] and [Au 2 (cAAC) 2 ] ( 27 ), each containing an M–M bond according to calculations.…”

“…By and large, the bonding and electronic situations of these complexes are rather unpredictable without the combination of experimental and theoretical studies. Because of their electronic configurations (d 5 to d 9 and d 10 s 1 ) the Cr I , Mn 0 , Fe 0 , Co 0 , and Cu 0 /Au 0 compounds 17 , 18 , 19 , 20 , and 22 / 23 , respectively, are paramagnetic, and the magnetic susceptibility measurements suggest S = 5/2 (Cr + ), 3/2 (Mn), 1 (Fe), 1/2 (Co), 1/2 (Cu), and 1/2 (Au) spin ground states for the corresponding [M(cAAC) 2 ] n + compounds. Although this correlates well with the expected values for chromium(I), iron(0), and colbalt(0) complexes 17 , 19 , and 20 , respectively, prediction of the spin ground state on the basis of linear coordination of zero oxidation state metals with given d‐electron configuration fails for manganese, copper, and gold complexes 18 , 22 , and 23 , respectively (Figure ).…”

Reduction of 2,2′-Bipyridine by Quasi-Linear 3d-Metal(I) Silylamides—A Structural and Spectroscopic Study

“…Complexes with two-coordinate 3d-metal(I) ions are a rare class of molecules in coordination chemistry [1][2][3][4][5][6][7][8][9][10][11][12][13]. They combine an uncommon coordination motif with an, for these metals, unusual oxidation state (with the exception of Cu and to a certain extent nickel).…”

Recent progress on NHC-stabilized early transition metal (group 3–7) complexes: Synthesis and applications

“…98 Notably, CAAC ligands were also used to stabilize an unprecedented two-coordinate Cr(I) cation [(CAAC)2Cr] + . 99 The complex was prepared by reduction of Cr(II) complex (CAAC)2CrCl2 with KC8 to yield (CAAC)2CrCl followed by treatment with…”