Electrophilic and nucleophilic addition reactions of Ir(1-2,5-η-CH2CHCHCHSO2)(PMe3)3 with HBF4, acetonitrile, CO, pyridine and methanol: Haptotropic behavior of the butadienesulfonyl ligand

Abstract

Reaction of IrCl(PMe3)3 with one equivalent of K(SO2CHCHCHCH2) led to the formation of Ir(1-2,5-η-CH2CHCHCHSO2)(PMe3)3 (1). The reaction of 1 with HBF4⋅Et2O takes place rapidly at low temperature to give the metallacycle [Ir(2,5-η-MeCHCHCHSO2)(PMe3)3]BF4 (2). Complex 2 reacts with CH3CN, CD3CN and CO to give the corresponding adducts [Ir(2,5-η-MeCHCHCHSO2)(PMe3)3(L)]BF4 (L = CH3CN, 3; CD3CN, 3D; CO, 4). Interestingly, compound 2 in the presence of pyridine or deuterated pyridine isomerizes to the terminal allyl compound [Ir(1-3,5-η-CH2CHCHCH2SO2)(PMe3)3]BF4 (5), while in the presence of oxygenated solvents, such as methanol, acetone and water, or their corresponding deuterated solvents, affords a mixture of cationic internal allyl isomers [Ir(2-4,6-η-MeCHCHCHSO2)(PMe3)3]BF4 (6a) and [Ir(2-4,5-η-MeCHCHCHSO2)(PMe3)3]BF4 (6b), being 6a always the major isomer. The iridium center is coordinated to an oxygen atom of the sulfone moiety in 6a, while for 6b coordination through the sulfur atom is proposed. Single-crystal X-ray diffraction studies of 5 and 6a confirm the unprecedented formation of novel sulfone-pentenyl ligands bonded to the iridium center through an η3 interaction and also by S and O coordination affording six-membered pseudo-ring structures. The mechanism of the formation of 5 and the mixture of isomers 6a and 6b is discussed. A comparative study with the thiapentadienyl analogue Ir(1-2,5-η-CH2CHCHCHS)(PMe3)3 (1S) is also considered.