Ethylene Substitution in a Bis-Ethylene Complex of Rh/Os and Unusual Brønsted−Lowry Basicity of an N-Heterocyclic Carbene

Abstract

Reactions of the bis-ethylene complex [RhOs(η2-C2H4)2(μ-CO)2(dppm)2][CF3SO3], with CO, MeCN, PMe3, IMe4, and [PPN][Cl] (IMe4 = 1,3,4,5-tetramethylimidazol-2-ylidene; PPN+ = bis(triphenylphosphine)iminium) yield the monoethylene products [RhOsL(C2H4)(μ-CO)2(dppm)2][CF3SO3] (L = CO (2), MeCN (3), PMe3 (4), IMe4 (5)) and [RhOsCl(C2H4)(μ-CO)2(dppm)2] (6), respectively, by substitution of the Rh-bound ethylene ligand. In the case of L = CO, carbon monoxide was added at −78 °C, since at higher temperatures substitution of both ethylene ligands occurred to give the known product [RhOs(CO)4(dppm)2][CF3SO3]. For L = IMe4, the stoichiometry had to be carefully controlled, since in the presence of more than 1 equiv of IMe4 deprotonation of a dppm methylene group by IMe4 occurred to yield [RhOs(IMe4)(C2H4)(μ-CO)2(Ph2PCHPPh2)(dppm)]. The IMe4 product (5) could also be obtained in THF solution by substitution of the acetonitrile ligand in compound 3. However, when this reaction was carried out in acetonitrile, deprotonation of the acetonitrile ligand by IMe4 occurred to give the acetonitrilide intermediate [RhOs(NCCH2)(C2H4)(μ-CO)2(dppm)2], which rapidly coupled with another 1 equiv of 3 to yield the enamino−nitrile-bridged product [(RhOs(C2H4)(μ-CO)2(dppm)2)2(μ-NHC(CH3)CHCN)][CF3SO3].

Unusual Ligand Transformations Initiated by dppm Deprotonation in Methylene-Bridged Rh/Os Complexes

“…This dichotomic behavior of IMe 4 has recently been observed by us in a number of closely related complexes of Rh/Os, in which deprotonation of either acetonitrile, methyl, or dppm ligands had occurred under some conditions, while conventional coordination of IMe 4 to Rh had occurred under others . We were therefore interested in determining the conditions under which IMe 4 would function as a conventional ligand and under which its Brønsted basicity would predominate.…”

“…The 89 Hz intraligand coupling ( 2 J P A −P B ) across the dppm bridge is normal; however, the intraligand 31 P− 31 P coupling across the Ph 2 P C CHP D Ph 2 bridge, at 21 Hz, is significantly less than that for the dppm group and much less than has previously been observed in dppm-H compounds (ca. 140 Hz) in which this ligand maintains a μ-κ 1 :κ 1 geometry, binding to each metal via P. ,, …”

Adsorption and Reactions of ICH2CN on Cu(100) and O/Cu(100)

“…Scheme d shows the N-bonded CH 2 CN with two cumulated double bonds. In terms of the reported CH 2 CN-containing metal complexes, CH 2 CN can be bonded to various metal centers, such as Hg, Rh, Co, Ni, La, Pt, Cu, Ag, and Au, and so forth. − For most of the metal complexes, CH 2 CN is C-metalated (M–CH 2 CN), with the CN as terminal noncoordinated group. However, in the crystal structure of [Cp 2 *LaCH 2 CN] 2 , the two Cp 2 *La units are connected by the bridging CH 2 CN groups (M–CH 2 CN–M) .…”

Study of the Reactivity of the [(PE1CE2P)Ni(II)] (E1, E2 = O, S) Pincer System with Acetonitrile and Base: Formation of Cyanomethyl and Amidocrotononitrile Complexes versus Ligand Decomposition by P–S Bond Activation

“…3-Amidocrotononitrile is a rather unusual ligand for transition metal complexes; however, examples are known in which two of these ligands bind to two metal centers via the amide and nitrile nitrogen atom. − Apart from that, only one Zn complex exists, where 3-amidocrotononitrile does not act as a bridging ligand, only coordinating via the amido nitrogen to the metal center . The complexes presented herein are, to the best of our knowledge, the first examples of fully characterized metal pincer complexes, where 3-amidocrotononitrile coordinates as a monodentate ligand to a single metal center.…”