Regioselective Formation of β‐Alkyl‐α‐phenyliridabenzenes via Unsymmetrical 3‐Vinylcyclopropenes: Probing Steric and Electronic Influences by Varying the Alkyl Ring Substituent

Abstract

The synthesis of unsymmetrical (Z)-1-alkyl-3-(2-iodovinyl)-2-phenyl-1-cyclopropenes (R=Me (8 a), Et (8 b), iPr (8 c), and tBu (8 d)) and their reactions with Vaska's complex [Ir(CO)Cl(PPh3)2] and its trimethylphosphine analogue [Ir(CO)Cl(PMe3)2] were investigated. Iridabenzvalene (13/20), iridabenzene (14/21), and/or eta(5)-cyclopentadienyliridium complexes (15/22) were obtained in modest yields and were fully characterized by spectroscopic means. X-ray structural data was secured for iridabenzvalene 13 d and iridabenzenes 14 a,b,d. Whereas iridabenzenes 14 a-c were stable at 75 degrees C for 48 h, 14 d, which possesses a bulky tBu group, rearranged cleanly to cyclopentadienyliridium 15 d at 50 degrees C over 15 h and displayed first-order kinetics. The influence of the alkyl substituent on the mechanisms of iridacycle generation, isomerization, and iridabenzene regioselectivity is discussed.

Recent Advances in Metallabenzene Chemistry

“…[66,68] As in the previous work, iridabenzvalenes such as 75 and 79 are formed in addition to iridabenzenes depending not on the phosphine, but on the nature of the R group. In certain cases, isomerization to the iridabenzene was found to be highly regioselective, forming the ortho-phenyl isomer 76 over the meta-phenyl isomer 77.…”

“…[64][65][66][67][68] In this case, several different ligands and metal complexes were used to produce a variety of structurally related iridabenzenes. This method of synthesis, which was inspired by the aforementioned studies from Hughes and coworkers, is derived from the well-known reactivity of cyclopropenes to form vinyl carbenes.…”

“…[33,67,68] One pathway begins by dissociation of the cyclopropene from the metal center and subsequent oxidative addition to generate Dewar benzene 74, which quickly rearranges into 71. Evidence for this pathway lies in the ability of donor solvents to rapidly increase the rate of isomerization.…”

Recent Advances in Metallaaromatic Chemistry

“…Since these early reports the study of metallabenzenes has flourished. [39][40][41][42][43][44] The third row transition metalsa re well-represented with examples incorporating osmium, [45][46][47][48][49][50][51][52][53][54][55][56][57][58][59][60][61] iridium, [62][63][64][65][66][67][68][69][70][71][72][73][74][75][76][77][78][79][80] platinum [81][82][83][84] and, most recently,r henium. [85][86][87] Metallabenzenes of one second row transition metal, ruthenium, are also known.…”

C–H Activation of 3,3-diphenylcyclopropene in the reaction with Os(CO)2(PPh3)3: 3,3-diphenylcyclopropenyl, 2,2-diphenylcyclopropyl, and 3-phenylindenyl complexes of osmium(II)

“…Crystal structures for several of these iridabenzvalene and rhodabenzvalene complexes have been reported [14][15][16][17]. A related structure has been reported for molybdenum(II), where the cyclopropene is tethered to the metal by a carboxylate group [18].…”