Synthesis and Structural Characterization of Palladium(II) Mixed-Ligand Complexes of N-(Benzothiazol-2-yl)benzamide and 1,2-Bis(diphenylphosphino)ethane.

Three novel palladium(II) mixed-ligand complexes of N-(benzothiazol-2-yl)benzamide (HL) and 1,2-bis(diphenylphosphino)ethane (dppe), [Pd(HL)(dppe)]Cl2 (1), [Pd(L)(dppe)]Cl (2), and [Pd(L)2(dppe)] (3), were synthesized and fully characterized using Fourier transform infrared, 1H, 13C, and 31P NMR, and molar conductivity measurements. Complex 3 was characterized by single-crystal X-ray diffraction. The ligand HL showed three different coordination modes: a neutral bidentate chelate bound through the endocyclic nitrogen and exocyclic oxygen atoms in 1, a negatively charged L bound as a bidentate chelate through the endocyclic nitrogen and negatively charged exocyclic oxygen atoms in 2, and a monodentate bound through the negatively charged endocyclic nitrogen atom in 3.

Synthesis, structure and reactivity with phosphines of Hg(II) ortho-cyano-aminothiophenolate complexes formed via C-S bond cleavage and dehydrogenation of 2-aminobenzothiazoles.

Addition of 2-aminobenzothiazole (abt) and substituted derivatives to Hg(OAc)2 leads to the high yield formation of ortho-cyano-aminothiophenolate (ocap) complexes [Hg{SC6H3XN(CN)}]n (X = H, Me, Cl, Br, NO2) resulting from dehydrogenation and C-S bond cleavage. The reaction appears to be unique to Hg(OAc)2 and with HgCl2 the product [HgCl2(abt)]n contains an intact abt ligand, but reacts with acetate to afford the ocap complex [Hg{SC6H4N(CN)}]n. Binding of abt to Hg(II) has previously been probed in molecular structures of [Hg(sac)2(abt)L] (L = MeOH, DMSO) and these have been reexamined to understand the perturbation of abt upon coordination. When the reaction of abt and Hg(OAc)2 was carried out at low temperatures the intermediate [Hg(κ2-OAc)(EtOH)(µ-HNCNSC6H4)]2 was isolated resulting from a single ligand deprotonation thus allowing a mechanism for ring-opening to be proposed. Reactions of [Hg{SC6H3XN(CN)}]n with mono- and bidentate phosphines have been studied, affording a series of complexes in which the ocap ligands adopt four different binding modes in the solid state, as shown by a number of crystallographic studies. In all, the ligand chelates to a single mercury centre but spans to the second via either: (i) a simple S,N-chelate, (ii) coordination through nitrogen of the CN group, (iii) the sulfur acting as a thiolate-bridge, (iv) both thiolate bridging and cyanide coordination. With PPh3 two different binding modes are seen in complexes [Hg{SC6H3XN(CN)}(PPh3)]2 being dependant upon the nature of the arene-substituent, while addition of excess PPh3 affords mononuclear [Hg{SC6H3XN(CN)}(PPh3)2]. With dppm, binuclear [Hg{SC6H3XN(CN)}(κ1-dppm)]2 result in which the diphosphine binds in a monodentate fashion. With the more flexible diphosphines, dppe and dppb, coordination polymers [Hg{SC6H3XN(CN)}(κ1,κ1-diphosphine)]n result in which ocap binds in a simple chelate fashion. Somewhat unexpectedly, with dppp, binuclear complexes [Hg2{SC6H3XN(CN)}2(µ,κ1,κ1-dppp)] result in which two diphosphines bridge the Hg2 centre, while with dppf mononuclear chelates are proposed to result. Thus, the simple and high-yielding ring-opening of 2-aminobenzothiazole and substituted derivatives by mercuric acetate provides ready access to a range of novel ortho-cyano-aminothiophenolate complexes, being shown to be a highly versatile ligand that can adopt a number of different coordination modes.

Palladium(II) ortho-cyano-aminothiophenolate (ocap) complexes.

A series of Pd(II) complexes containing ortho-cyano-aminothiophenolate (ocap) ligands have been prepared and their molecular structures elucidated. Hg(II) ocap complexes, [Hg{SC6H3XN(CN)}]n (X = H, Me) (1), react with Na2S to afford HgS and Na2[ocap] which reacts in situ with K2[PdCl4] to afford palladium ocap complexes [Pd{SC6H3XN(CN)}]n (2). A second route to these coordination polymers has also been developed from reactions of 2-aminobenzothiazole (abt) complexes, trans-PdCl2(abt)2 (3), with NaOH. We have not been able to crystallographically characterise coordination polymers 2, but addition of PPh3, a range of phosphines and cyclic diamines affords mono and binuclear complexes in which the ocap ligand adopts different coordination geometries. With PPh3, binuclear [Pd(µ-κ2,κ1-ocap)(PPh3)]2 (4) results, in which the ocap bridges the Pd2 centre acting as an S,N-chelate to one metal centre and binding the second via coordination of the cyanide nitrogen. In contrast, with diphosphines, Ph2P(CH2)nPPh2 (n = 1-4), mononuclear species predominate as shown in the molecular structures of Pd(κ2-ocap){κ2-Ph2P(CH2)nPPh2} (5-7; n = 1-3). With 2,2'-bipy and 1,10-phen we propose that related monomeric chelates Pd(κ2-ocap)(κ2-bipy) (9) and Pd(κ2-ocap)(κ2-phen) (10) result but we have been unable to substantiate this crystallographically. Addition of HgCl2(phen) to 9a (generated in situ) affords heterobimetallic Pd(κ2-phen)(µ-κ2,κ1-ocap)HgCl2(κ2-phen) (11), in which Hg(II) is coordinated through the ring sulfur.

Formation of ortho-cyano-aminothiophenolate ligands with versatile binding modes via facile carbon-sulfur bond cleavage of 2-aminobenzothiazoles at mercury(II) centres.

Addition of 2-aminobenzothiazole and substituted derivatives to mercuric acetate in warm ethanol leads to the high yield formation of [Hg{SC6H3XN(C[triple bond, length as m-dash]N)}]n resulting from loss of hydrogen and sulfur-carbon bond cleavage. Addition of phosphines affords a series of complexes in which the new ortho-cyano-aminothiophenolate ligands adopt three different binding modes.