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...

Oxidative addition of cyclic alkyl(amino)carbenecoordinated phosphinidenes (Me cAAC)PX to LGa affords gallium-coordinated phosphinidenes LGa(X)-P(Me cAAC) (L = HC[C(Me)N(2,6-i-Pr 2 C 6 H 3)] 2 ;X = Cl 1,B r2), which react with NaBAr F 4 and LiAl(OR F) 4 to [LGaP(Me cAAC)][An] (An = B(C 6 H 3 (CF 3) 2) 4 3,B (C 6 F 5) 4 4,A l(OC(CF 3) 3) 4 5). The cations in 3-5 show substantial Ga À Pd ouble bond character and represent heteronuclear analogues of allyl cations according to quantum chemical calculations.The reaction of 4 with 4dimethylaminopyridine (dmap) to adduct 6 confirms the strong electrophilic nature of the gallium center,w hereas 5 reacts with ethyl isocyanate with C À Cbond formation to the g-Ca tom of the b-diketiminate ligand and formation of compound 7. Scheme 1. Structurallyc haracterized cations A-F (E:R= I, H, Me, Et); F:R= Si(i-Pr)[CH(SiMe 3) 2 ] 2); A, D:E= Si, Ge) and resonance structures of allyl and heavier homologues.

The neutral radical (Me -cAAC) AlCl (2) is stabilized by cyclic (alkyl)(amino)carbenes (cAACs). Complex 2 was synthesized by reduction of the Me -cAAC:→AlCl (1) adduct with KC in the presence of another equivalent of Me -cAAC. The crystal structure of 2 shows that the Al-C bond lengths of the two carbenes bound to the Al center are considerably different, which is likely the result of intermolecular interactions. Quantum-chemical calculations from the gas phase give an equilibrium structure with identical Al-C bond lengths. Compound 2 exhibits monoradical character, which was confirmed by EPR measurements. A bonding analysis indicates that the unpaired electron resides mainly at the carbene carbon atoms. Compound 2 is an example for an unusual neutral Al radical.

The cyclic alkyl(amino) carbene-anchored silylene-phosphinidene was isolated as L-Si-P(:cAAC-Me) (L=benzamidinate) at room temperature, synthesized from the reduction of L-Si(Cl )-P(:cAAC-Me) (1) using two equivalents of KC . Compound 1 was prepared by the oxidative addition of a chlorophosphinidene to the benzamidinate substituted silylene center. This is the first molecular example of a silylene-phosphinidene characterized by single-crystal X-ray structural analysis. Moreover, H, P, and also Si NMR spectroscopic data supported the formulation of the products. The theoretical calculations of compound 2 are in good agreement with the experimental results.