ELSEVIER InorganicaChimicaAcla250 ( i 996) 283-294 Light induced sulfur-dealkylation of phosphino-thioether nickel (0) complexes Jang Sub Kim, Joseph H. Reibenspies, Marcetta Y. Darensbourg * Departmentof Chemistry, TexasA&M University,CollegeStation. TX 77843. USA Received 6 February 1996; revised 16May 1996 Abstract The observation of homolytic S-CH~ bond cleavage in (Ph2P(o-C6H4)SCH3)2Ni ° under photochemical conditions has promptnd funl~r investigation of nickel(0) complexes and their stability. Tetradentate P2S'2 donor ligands (S' .-= thioether type S donor) with aromatic rin~ incorporated into the P to S links, Ph2P(o-C6H4)S(CH2)3S(o-C6H4)PPh2 (arom-PSSP), or the S to S links, Ph2P(CH2)2SCHa(o- C6H4)CH2S(CH2) 2PPh2 (PS-xy-SP), have been used to form four-coordinate,square planar nickel(ll) complexes, [ (arom-PSSP) Nil (BE02 (2) and [(PS-xy-SP)Ni](BF4)2 (3). The bidentate and tetradentate ligands, Ph2P(o-C6H4)SCH2CH 3 (arom-PSEt) and Ph2P(CH2)2S(CH2)3S(CH2)2PPh2 (PSSP), give similar complexes, [ (arom-PSFA)2Ni](BF4)2 (1) and [(PSSP)Ni] (BF4)2 (4), respec- tively. Cyclic voltammograms of the Niu complexes in CH3CNshow two reversible redox events assigned to Ninn and Nim/°. The one-electron reduction product produced by stoiehiometric amounts of Cp2Co can be characterized by EPR. At I00 K rhombic signals show hyperiine coupling to two phosphorus atoms. Complete bulk chemical reduction of complexes 1, 2, 3 and 4 with Na/Hg amalgam provided the corresponding nickel(O) complexes 1 n, 2a, 3~ and 4R which were isolated as red solutions or solids and characterized by magnetic resonance properties and reaction products. Photolysis of these nickel(0) complexes leads to S-dealkylafionto produce alkyl radicals and dithiolate nickel(I1) complexes. Complex 3 crystallized in the monoclinic space group P2=lc with a =20.740(5), b=9.879(3), c= 17.801(4) A, ~--92.59(2) °, V=3644(2) A3 and Z=4; complex 4: P2~lc with a--13.815(4), b=13.8!5~,4), c=15.457(5) A, ~= 104.89(2) °, V= 3365.4(14) A3 and Z=4. Keywords: Crystal structures;Sulfurdealkylation;Nickelcomplexes; Phosphino-thioether complexes 1. Introduction We recently reported the X-ray crystal structure and light- induced S-demethylation of the (arom-PSMe)2Ni ° complex (Scheme 1, arom-PSMe = Ph2P(o-CtH4)SMe) which was prepared by the chemical reduction of [(arom- PSMe)2Ni] (BF4)2 [ 1]. Interestingly, the latter, the parent nickel(II) complex, is light stable, but is unstable towards heterolytic C-S bond cleavage by nucleophiles such as iodide ion. The nucleophilic displacement of carbonium ions from Group VIII metal-bound thioethers in P2S'2 ligation is a well known reaction and kinetic studies have established an asso- ciative mechanism [2]. Both routes to C-S bond cleavage result in the stable dithiolate nickel(II) complex, (arom- PS)2Ni n (7) (arom-PS-- Ph2P(o-CtH4)S- ) [ 1,2b]. HomoIytic S-C bond cleavage reactions of the thioether ligand in reduced metals [3,4] have been used as functional models for the nickel-containing cofactor of methyl-coen- * Cogresponding author. 0020-1693/96/$15.00© 1996 Elsevier Science S.A. All rights reserved PI! S0020-1693 ( 96 ) 05237- I HaG p .7 2. 7 CH3 [I=~om4=S~).~f* Scheme I. zyme M reductase (Me-CoM red,erase), an enzyme which serves to catalyze the formation of methane from CO2 and H2 [5,6]. The cofactor, the nickel tetrahydrocorphinoid (NiF43o), is involved in the C-S cleavage of methylthio- ether-2- (methylthio) ethanesuifonate (methyl-coenzyme M=Me-CoM) with 7-mercaptoheptanoyl threonine phos-