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) in THF, 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 insertion products (triphos)IrH(è2(C,S)-C20H12S) (3a,b; triphos ) MeC(CH2PPh2)3). In the temperature range from 70 to 100 °C, the reaction gives kinetic mixtures of the C-S insertion products and of the complex (triphos)IrH(è2-C20H12S) (2), which is suggested to contain an intact DNT molecule bound to iridium via a double bond from a naphthyl ring. Complex 2 in THF transforms into 3a,b even at 70 °C. Hydrogenation of 3a,b (30 atm of H2, 60 °C) in THF gives the dihydride thiolate complex (triphos)Ir(H)2(SC20H13), which is protonated by strong acids, converting to the dimer [(triphos)IrH(í-SC20H13)2HIr(triphos)](BPh4)2. The latter compound 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 thiolate product (triphos)Rh(H)2(SC20H13). The latter complex reacts in THF with KOBut in the presence 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 the homogeneous 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 added base plays a dual role: it serves to generate the catalyst from the precursor and accelerates the reaction rate by influencing the rate-determining step positively.