EXPERIMENTAL AND THEORETICAL INVESTIGATIONS OF THE FORMATION OF THE DIAZENE PHSN=C(H)N=NC(H)=NSPH FROM HCN2(SPH)(3) BY A THIYL-RADICAL-CATALYZED MECHANISM - IDENTIFICATION OF THE HC(NSPH)2(CENTER-DOT) RADICAL AND X-RAY STRUCTURES OF HCN2(SPH)(3) AND PHSN=C(H)N=NC(H)=NSPH

The reaction of HCN2(SiMe(3))(3) with benzenesulfenyl chloride in a 1: 3 molar ratio produces HCN2(SPh)(3) (4) as thermally unstable, colorle ss crystals. The decomposition of (4) in toluene at 95 degrees C was m onitored by UV-visible, H-1 NMR and ESR spectroscopy. The major final products of the decomposition were identified as PhSN=C(H)N=NC(H)=NSPh (5) and PhSSPh. The structures of 4 and 5 were determined by X-ray cr ystallography. The crystals of 4 are monoclinic, space group P2(1)/a, with a = 9.874(2) Angstrom, b = 19.133(2) degrees, c = 10.280(2) Angst rom, beta = 113.37(1)degrees, V = 1782.8(5) Angstrom(3), and Z = 4. Th e final R and R(w) values were 0.042 and 0.049, respectively. The crys tals of 5 are monoclinic, space group P2(1)/n, with a = 5.897(6) Angst rom, b = 18.458(10) Angstrom, c = 7.050(8) Angstrom, beta = 110.97(5)d egrees, V = 716(1) Angstrom(3), and Z = 2. The final R and R(w) values were 0.075 and 0.085, respectively. The diazene 5 adopts a Z,E,Z stru cture with weak intramolecular S ... N contacts of 2.83 Angstrom, givi ng rise to four-membered NCNS rings. During the thermolysis of 4 at 95 degrees C in toluene a transient species (lambda(max) 820 nm) was det ected. It decomposes with second-order kinetics to give 5 (lambda(max) 450 nm). The ESR spectrum of the reaction mixture consisted of the su perposition of a three-line 1:1:1 spectrum (g = 2.0074, A(N) = 11.45 G ), attributed to (PhS)(2)N-., upon a doublet of quintets (1:2:3:2:1) w ith g = 2.0070, A(N) = 6.14 G, A(H) = 2.1 G assigned to the radical HC N2(SPh)(2)(.). Density functional theory (DFT) calculations for the mo dels of the radical showed the E,Z isomer to have the lowest energy. T hermochemical calculations indicate that the decomposition of HCN2(SH) 3 into the diazene (Z,E,Z)-HSN=C(H)N=NC(H)=NSH (and 2 HSSH) is substan tially more exothermic (Delta H = -176.1 kJ mol(-1)) than the correspo nding formation of the isomeric eight-membered ring (HC)(2)N-4(SH)(2) (Delta(H) = -40.6 kJ mol(-1)). These calculations also indicate that t he diazene is formed by a mechanism in which the RS(.) radical acts as a catalyst.