The cyclic alkyl(amino) carbene (cAAC) bonded chlorophosphinidene (cAAC)PÀCl (2/2')w as isolated from the direct reaction between cAAC and phosphorus trichloride (PCl 3 ). Compound 2/2' has been characterizedb y NMR spectroscopy and mass spectrometry. 31 PNMR investigations [d % 160 ppm (major) and d % 130 ppm (minor)] reveal that there are two different Pe nvironments of the PÀCl unit. X-ray single-crystal determinations uggests ac o-crystallization of two conformational isomers of (cAAC)PÀCl (2/2'); the major compound possessing ac AACÀPCl unit with C cAAC ÀP1 .75 .T his CÀPb ond length is very close to that of (NHC) 2 P 2 [NHC = N-heterocyclic carbene].T he residual density can be interpreted as ac onformational isomer with as horter C cAAC ÀPb ond similar to an on-conjugated phosphaalkene [RÀP=CR 2 ]. Our study shows an unprecedented example of two conformational isomersw ith different C carbene Àelementb onds. Additionally,B r( 3c/3c'), I( 4c/4c'), and H( 5c/5c')a nalogues [(Me 2 -cAAC)PÀX; X= Br (3), I( 4), H( 5)] of 2c/2c'[(Me 2 -cAAC)PÀCl] were also synthesized and characterized by NMR spectroscopy suggesting similare quilibrium in solution. The unique property of cAAC and the required electronegativity of the X( X= Cl, Br,I ,a nd H) atom play ac rucial role for the existence of the two isomersw hichw ere further studied by theoretical calculations.Since the synthetic reports of stable and isolable singlet Nheterocyclic carbenes (NHCs) in 1988 by Bertrand et al. [1] and in 1991 by Arduengo et al., [2] syntheses and characterization of severals table carbenes have been reported. [3] The use of carbenes has brought numerousb reakthroughs in the field of homogenous catalysis [4] and NHCs have been utilized as strong s-donors in different fields of chemistry. [5] The carbene carbon atom of an NHC is bound to two s-withdrawing and p-donating nitrogen atoms. [5] Consequently,t he accumulationo fe lectron density in the p z -orbital of the carbenec arbon atom is reasonably high leading to the weak p-accepting property of NHC. [6] Theoretical studies as well as experimental evidence have shown that non-negligible p-back-donation occurs in the bondingb etween NHCs and transition metals. [7] The syntheses of cyclic alkyl(amino)c arbenes (cAACs) [8] were reported in 2005 by Bertrande tal. One s-withdrawing and p-donating nitrogen atom of an NHC is replaced by a s-donating quaternary carbon atom in cAAC leading to al ower lying LUMO. cAACs are superior ligands for the stabilization of various unstable chemicals pecies, [9] radicals, [10] and elements in their different oxidation states [11] due to their stronger p-accepting properties. This is energetically advantageous for acceptance of pback donation from the element bound to the carbene carbon atom (C cAAC )o fc AAC (see the Supporting Information). [3b, 12, 13] The electronic properties of C cAAC and the accumulation of electron densities on the elements (E) are very important since they control the chemical behavior of the cAAC-containing compo...

The first acceptor-free heavier germanium analogue of an acylium ion, [RGe(O)(NHC) 2 ]X (R = Mes Ter= 2,6-(2,4,6-Me 3 C 6 H 2 ) 2 C 6 H 3 ; NHC = IMe 4 = 1,3,4,5-tetramethylimidazol-2-ylidene; X = (Cl or BArF= {(3,5-(CF 3 ) 2 C 6 H 5 ) 4 B}), was isolated by reacting [RGe(NHC) 2 ]X with N 2 O. Conversion of the germa-acylium ion to the first solely donor-stabilized germanium ester [(NHC)RGe(O)(OSiPh 3 )] and corresponding heavier analogues ([RGe(S)(NHC) 2 ]X and [RGe(Se)(NHC) 2 ]X) demonstrated its classical acylium-like behavior. The polarized terminal GeO bond in the germa-acylium ion was utilized to activate CO 2 and silane, with the former found to be an example of reversible activation of CO 2 , thus mimicking the behavior of transition metal oxides. Furthermore, its transition metal like nature is demonstrated as it was found to be an active catalyst in both CO 2 hydrosilylation and reductive N-functionalization of amines using CO 2 as C 1 source. Mechanistic studies were undertaken both experimentally and computationally, which revealed the reaction proceeds via a NHC-siloxygermylene [(NHC)RGe(OSiHPh 2 )].

Recent years have witnessed a growing interest in the development of efficient copper-based catalytic systems following the Chan−Lam (CL) reaction protocol for the C−N bond formation. Though CL amination has been widely explored experimentally, it is quite underdeveloped from a mechanistic standpoint. Extensive theoretical investigations are carried out to unravel the mechanistic pathways of the CL reaction. We report in detail the fundamental reaction steps involved in Cu-catalyzed carbon−heteroatom bond formation reactions, particularly the CLbased amination. An in-depth examination of this study provides some interesting insights into little known pathways such as the denucleation of dimeric copper acetate, the disproportionation of the Cu(II) complex, and the regeneration of Cu(II) from Cu(I) intermediates. The rate-determining step of 26.0 kcal mol −1 involves the disproportionation and reductive elimination of the Cu(II) intermediate. The mechanism for the inhibitory effect of pinacol (BPin) esters, off-cycle reaction routes, and influence of amine substrates are elaborated in this context. For a series of heteroarene substrates, it was observed that the catalyst generation energy span correlates with the experimentally observed reaction outcome. The calculated results are in agreement with the experimental observations based on spectroscopic and kinetic studies.

Two cyclic (alkyl)(amino)carbene (cAAC) stabilized mononuclear neutral radicals of aluminum have been synthesized. They contain an ethyl [(cAAC)AlClEt (1)] and as well a diethyl group [(cAAC)AlEt (2)], and have been prepared from the reduction of EtAlCl and EtAlCl, respectively, with KC. Compounds 1 and 2 are monoradicals, which were confirmed by EPR measurements to have the spin located on the carbene carbon of one of the cAAC ligands.

Bis-NHC stabilized germyliumylidenes [RGe(NHC) 2 ] + are typically Lewis basic (LB) in nature, owing to their lone pair and coordination of two NHCs to the vacant p-orbitals of the germanium center. However, they can also show Lewis acidity (LA) via GeÀ C NHC σ* orbital. Utilizing this unique electronic feature, we report the first example of bis-NHCstabilized germyliumylidene [ Mes TerGe(NHC) 2 ]Cl (1), ( Mes Ter = 2,6-(2,4,6-Me 3 C 6 H 2 ) 2 C 6 H 3 ; NHC = IMe 4 = 1,3,4,5-tetramethylimidazol-2-ylidene) catalyzed reduction of CO 2 with amines and arylsilane, which proceeds via its Lewis basic nature. In contrast, the Lewis acid nature of 1 is utilized in the catalyzed hydroboration and cyanosilylation of carbonyls, thus highlighting the versatile ambiphilic nature of bis-NHC stabilized germyliumylidenes.