HDS MODEL SYSTEMS - COORDINATION, OPENING, AND HYDROGENATION OF BENZO[B]THIOPHENE AT IRIDIUM

The eta 4-benzene complexes [(triphos)Ir(C6H6)]Y (Y = BPh(4), 1a; PF6, 1b) react with benzo[b]thiophene (BT) at room temperature to give the unprecedented [(triphos)Ir(eta(3)-C,C,S-C8H6S)]Y (Y = BPh(4), 2a; PF6 , 2b) in which intact BT is coordinated to the metal center through th e S atom and the C-2=C-3 bond. 2a and 2b are transformed upon mild the rmolysis into the iridabenzothiabenzene complexes [(triphos)Ir(eta(2)- C,S-C8H6S)]Y (Y = BPh(4), 3a; PF6, 3b). An X-ray analysis has been car ried out on 3a.1.5THF.0.5EtOH. The coordination geometry around iridiu m may be described as a distorted trigonal-bipyramid, the metal center being surrounded by the three phosphorus atoms of triphos and by a ca rbon and a sulfur atom from a CS-cleaved BT molecule. Crystal data: tr iclinic, space group P (1) over bar, a 17.391(3) Angstrom, b = 16.957( 4) Angstrom, c = 12.795(3) Angstrom, alpha = 77.51(2)degrees, beta = 8 0.98(2)degrees, gamma = 75.50(2)degrees, Z = 2, d(calcd) = 1.31 g cm(- 3), n(obsd) = 7636, R = 0.072. Interaction of 2a with CO (1 atm, 20 de grees C) yields [(triphos)Ir(CO)(2)]BPh(4) (4) plus free BT, whereas 3 a requires more drastic conditions (5 atm, 70 degrees C) to eliminate BT and produce 4. 2a also reacts with H-2 (1 atm, 20 degrees C) to pro duce [(triphos)Ir(H)(2)(eta(1)-S-BT)]BPh(4) (5), which can be independ ently prepared by treatment of [(triphos)Ir(H)(2)(THF)]BPh(4) with BT; at 5 atm H-2, free BT is obtained together with [(triphos)Ir(H)(3)], BPh(3), and benzene, as a result of a heterolytic splitting of H-2 at the [(triphos)Ir(H)(2)](+) fragment assisted by the BPh(4)(-), counter anion. The C-S-cleaved BT in 3a is readily hydrogenated (5 atm, 20 deg rees C) to 2-ethylbenzenethiolate, producing [(triphos)Ir(H)(2){o-S-(C 6H4)C2H5}] (8) plus BPh(3) and benzene also via heterolytic splitting of H-2 assisted by BPh(4)(-), protonolysis of 8 with 2 equiv HCl produ ces (triphos)IrCl3 with concomitant liberation of 2-ethylbenzenethiol, a primary product of BT HDS. If the PF6- analogue 3b is used instead, the reaction with H-2 under identical conditions yields the thiolate- bridged dimer riphos)IrH{mu-o-S(C6H4)C2H5}2HIr(triphos)](PF6)(2) (9b). 3a also reacts with LiHBEt(3) to give [(triphos)Ir(H)(eta(2)-C,S-C8H6 S)] (11), which converts in THF solution at 66 degrees C into [(tripho s)Ir(eta(3)-S(C6H4)CH=CH2)] (12) by hydride migration to C-2; neither 11 nor 12 react with H-2 under mild conditions. Addition of HBF4.OEt(2 ) to 12 yields [(triphos)Ir(eta(4)-S(C6H4)C(H)Me)]BF4 (13c), which doe s react with H-2 even at 1 atm to give the thiolate-bridged dimer riph os)IrH{mu-o-S(C6H4)C2H5}2HIr(triphos)](BF4)(2) (9c). 13c also reacts w ith H- to give [(triphos)IrH(eta(2)-S(C6H4)C(H)Me)] (14), which in tur n reacts with H-2 and HBF4.OEt(2) to yield 8 and 9c, respectively.