Opening and hydrogenation of dinaphtho[2,1-b:1',2'-d]thiophene (DNT) by soluble rhodium 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 degrees C to give a temperature-invariant 3:2 mixture of the two diastereomeric C-S insertion products (triphos)IrH(eta(2)(C,S)-C20H12S) (3a,b; triphos = MeC(CH(2)PPh(2))(3)). In the temperature range from 70 to 100 degrees C, the reaction gives kinetic mixtures of the C-S insertion products and of the complex (triphos)IrH(eta(2)-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 degrees C. Hydrogenation of 3a,b (30 atm of H-2, 60 degrees 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(mu-SC(20)R(13))(2)HIr(triphos)](BPh(4))(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 degrees C) to give exclusively the dihydride thiolate product (triphos)Rh(H)(2)(SC20H13). The latter complex reacts in THF with KOBu(t) in the presence of H-2 (5 atm) at room temperature to give the trihydride 6 and potassium 1,1'-binaphthalene-2-thiolate. In the presence of a strong base (KOBu(t)), the pi-alkyne complex [(triphos)Rh(eta(2)-MeO(2)CC=CCO(2)Me)]PF6 in THF behaves as a catalyst precursor for the homogeneous hydrogenolysis of DNT to 1,1'-binaphthalene-2-thiol (30 atm of H-2, 160 degrees 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.