Opening and Hydrogenation of Dinaphtho[2.1-b:1'.2'-d]thiophene (DNT) by Soluble Rhodium and Iridium Complexes. Homogeneous Hydrogenolysis of DNT to 1,1¢-Binaphthalene-2-thiol by Rhodium Catalysis

The fragment [(triphos)IrH], generated in situ by thermolysis of (triphos)Ir(H)2(C2H5) inTHF, reacts with dinaphtho[2,1-b:1¢,2¢-d]thiophene (DNT) at temperatures higher than 100°C to give a temperature-invariant 3:2 mixture of the two diastereomeric C-S insertionproducts (triphos)IrH(è2(C,S)-C20H12S) (3a,b; triphos ) MeC(CH2PPh2)3). In the temperaturerange from 70 to 100 °C, the reaction gives kinetic mixtures of the C-S insertion productsand of the complex (triphos)IrH(è2-C20H12S) (2), which is suggested to contain an intact DNTmolecule bound to iridium via a double bond from a naphthyl ring. Complex 2 in THFtransforms into 3a,b even at 70 °C. Hydrogenation of 3a,b (30 atm of H2, 60 °C) in THFgives the dihydride thiolate complex (triphos)Ir(H)2(SC20H13), which is protonated by strongacids, converting to the dimer [(triphos)IrH(í-SC20H13)2HIr(triphos)](BPh4)2. The lattercompound is straightforwardly obtained by reaction of 3a,b with protic acids. The complex(triphos)RhH3 (6) reacts with DNT (THF, 70 °C) to give exclusively the dihydride thiolateproduct (triphos)Rh(H)2(SC20H13). The latter complex reacts in THF with KOBut in thepresence of H2 (5 atm) at room temperature to give the trihydride 6 and potassium 1,1¢-binaphthalene-2-thiolate. In the presence of a strong base (KOBut), the ð-alkyne complex[(triphos)Rh(è2-MeO2CCtCCO2Me)]PF6 in THF behaves as a catalyst precursor for thehomogeneous hydrogenolysis of DNT to 1,1¢-binaphthalene-2-thiol (30 atm of H2, 160 °C).In the proposed mechanism, the [(triphos)RhH] fragment acts as the catalyst while the addedbase plays a dual role: it serves to generate the catalyst from the precursor and acceleratesthe reaction rate by influencing the rate-determining step positively.