Amino-Substituted Butatrienes: Unusual η¹ Ligands Formed by an Unusual Reaction

Abstract

The reaction of the bis(amino)allenylidene complex [(CO) 5 WdCdCdC(NMe 2 ) 2 ] with diethyldiazomethane yields two products, a cyclic carbene complex (2) by 1,2-addition of Et 2 C-N 2 to the C R -C β bond of the allenylidene ligand and the η 1 -butatriene complex [(CO) 5 W{C[C(NMe 2 ) 2 ]d CdCEt 2 }] (3). Complex 2 slowly eliminates N 2 and rearranges into 3. In contrast, only η 1 -butatriene complexes, [(CO) 5 M{C[C(NMe 2 )XR]dCdC(R 0 ) 2 }], are isolated from the reaction of diazoalkanes (R 0 ) 2 C-N 2 (R 0 = Me, Et, n Pr) with alkoxy(amino)allenylidene complexes [(CO) 5 MdCd CdC(NMe 2 )OR] (M = Cr, W; R = Me, Et, (-)-menthyl) or with the (alkylthio)(amino)allenylidene complex [(CO) 5 WdCdCdC(NMe 2 )S n Pr]. These new η 1 -butatriene complexes are related to C R phosphine adducts of allenylidene complexes such as [(CO) 5 W{C(PMe 3 )dCd C(NMe 2 )Ph}] (17) and might be regarded as C R carbene adducts. However, the PMe 3 substituent in 17 is not replaced when 17 is treated with an N-heterocyclic carbene. Vice versa, the "carbene" substituent "C(NMe 2 )OEt" in the η 1 -butatriene complex [(CO) 5 Cr{C[C(NMe 2 )OEt]dCdCEt 2 }] is not replaceable by PMe 3 . Free N-heterocyclic carbenes do not add to the C R atom of the allenylidene complex [(CO) 5 WdCdCdC(C 6 H 4 NMe 2 -p) 2 ] but instead to the C γ atom, giving the dipolar neutral alkynyl complexes [(CO) 5 W-CtCC(C 6 H 4 NMe 2 -p) 2 L] (L = SIMe, SIMes). DFT calculations on the reaction mechanism indicate that a cyclic carbene complex and two isomeric η 2 -butatriene complexes are intermediates in the reaction pathway to form η 1 -butatriene complexes. The structure of two representative examples of η 1 -butatriene complexes and of one C γ carbene adduct has been established by X-ray structure analyses. † Dedicated to Professor J€ urgen Heck on the occasion of his 60th birthday.

Haptotropic Shift of [5]Cumulenes in Zirconocene Complexes and Effects of Steric Factors

“…Another isomer, 15a ″, is possible, but it is unlikely taking account of its steric congestion, and the third isomer was not detected as far as we investigated. This indicates that 15a and 15a ′ were in equilibrium in solution, and the equilibrium probably proceeded by “ligand-sliding”, not via 14a . ,, The “sliding” between 15a and 15a ′ is fast compared with the NMR time scale at rt.…”

Mesoionic and Related Less Heteroatom-Stabilized N-Heterocyclic Carbene Complexes: Synthesis, Catalysis, and Other Applications

“…Reaction of the bis(dimethylamino)allenylidene complex 427 with freshly prepared diethyldiazomethane, Et 2 C−N 2 , at room temperature proceeds slowly to afford the pyrazolylidene complex 428 and the η 1 -butatriene complex 429 as two major product fractions (Scheme 178). 345 pentacarbonyl complexes with ynamines. 346 In THF solution, complex 428 slowly eliminates N 2 and rearranges to 429, which limits the utility of this method to generate pyrazolylidene complexes.…”

“…Reaction of the bis­(dimethylamino)­allenylidene complex 427 with freshly prepared diethyldiazomethane, Et 2 C–N 2 , at room temperature proceeds slowly to afford the pyrazolylidene complex 428 and the η 1 -butatriene complex 429 as two major product fractions (Scheme ). Complex 428 results from cycloaddition of Et 2 C–N 2 to the C α –C β bond of the allenylidene ligand, presumably initiated by nucleophilic attack of the diazoalkane at C α of 427 . Similar cyclization reactions have been observed in the reaction of allenylidene pentacarbonyl complexes with ynamines .…”