[(η(6)-C(10)H(14))RuCl(μ-Cl)](2) (η(6)-C(10)H(14) = η(6)-p-cymene) was subjected to a bridge-splitting reaction with N,N',N''-triarylguanidines, (ArNH)(2)C═NAr, in toluene at ambient temperature to afford [(η(6)-C(10)H(14))RuCl{κ(2)(N,N')((ArN)(2)C-N(H)Ar)}] (Ar = C(6)H(4)Me-4 (1), C(6)H(4)(OMe)-2 (2), C(6)H(4)Me-2 (3), and C(6)H(3)Me(2)-2,4 (4)) in high yield with a view aimed at understanding the influence of substituent(s) on the aryl rings of the guanidine upon the solid-state structure, solution behavior, and reactivity pattern of the products. Complexes 1-3 upon reaction with NaN(3) in ethanol at ambient temperature afforded [(η(6)-C(10)H(14))RuN(3){κ(2)(N,N')((ArN)(2)C-N(H)Ar)}] (Ar = C(6)H(4)Me-4 (5), C(6)H(4)(OMe)-2 (6), and C(6)H(4)Me-2 (7)) in high yield. [3 + 2] cycloaddition reaction of 5-7 with RO(O)C-C≡C-C(O)OR (R = Et (DEAD) and Me (DMAD)) (diethylacetylenedicarboxylate, DEAD; dimethylacetylenedicarboxylate, DMAD) in CH(2)Cl(2) at ambient temperature afforded [(η(6)-C(10)H(14))Ru{N(3)C(2)(C(O)OR)(2)}{κ(2)(N,N')((ArN)(2)C-N(H)Ar)}]·xH(2)O (x = 1, R = Et, Ar = C(6)H(4)Me-4 (8·H(2)O); x = 0, R = Me, Ar = C(6)H(4)(OMe)-2 (9), and C(6)H(4)Me-2 (10)) in moderate yield. The molecular structures of 1-6, 8·H(2)O, and 10 were determined by single crystal X-ray diffraction data. The ruthenium atom in the aforementioned complexes revealed pseudo octahedral "three legged piano stool" geometry. The guanidinate ligand in 2, 3, and 6 revealed syn-syn conformation and that in 4, and 10 revealed syn-anti conformation, and the conformational difference was rationalized on the basis of subtle differences in the stereochemistry of the coordinated nitrogen atoms caused by the aryl moiety in 3 and 4 or steric overload caused by the substituents around the ruthenium atom in 10. The bonding pattern of the CN(3) unit of the guanidinate ligand in the new complexes was explained by invoking n-π conjugation involving the interaction of the NHAr/N(coord)Ar lone pair with C═Nπ* orbital of the imine unit. Complexes 1, 2, 5, 6, 8·H(2)O, and 9 were shown to exist as a single isomer in solution as revealed by NMR data, and this was ascribed to a fast C-N(H)Ar bond rotation caused by a less bulky aryl moiety in these complexes. In contrast, 3 and 10 were shown to exist as a mixture of three and five isomers in about 1:1:1 and 1·0:1·2:2·7:3·5:6·9 ratios, respectively in solution as revealed by a VT (1)H NMR, (1)H-(1)H COSY in conjunction with DEPT-90 (13)C NMR data measured at 233 K in the case of 3. The multiple number of isomers in solution was ascribed to the restricted C-N(H)(o-tolyl) bond rotation caused by the bulky o-tolyl substituent in 3 or the aforementioned restricted C-NH(o-tolyl) bond rotation as well as the restricted ruthenium-arene(centroid) bond rotation caused by the substituents around the ruthenium atom in 10.

Protonation of the amido groups of M(NMe 2 ) 5 (M = Ta or Nb) with trialkylguanidines, (RNH) 2 CNR (R = i-Pr or Cy), directly produced a series of five-co-ordinated complexes, M(NMe 2 ) 3 [(RN) 2 CNR] 1-4. Single crystal X-ray analysis confirmed that 1 contained a dianionic N,NЈ,NЉ-triisopropylguanidinate ligand which was co-ordinated in a chelating bidentate mode. In contrast, protonation of the amido groups of Ta(NMe 2 ) 4 Cl with triisopropylguanidine gave the six-co-ordinated complex Ta(NMe 2 ) 3 Cl[(i-PrN) 2 CNHi-Pr] 5 which possessed a bidentate monoanionic guanidinate ligand. Complex 5 can be converted into 1 by reaction with either LiNMe 2 or MeMgBr.

A one pot reaction involving sym N,N′-diarylthiourea and the respective arylamine in the presence of aq. KOH in nitrobenzene at ≥105°C afforded sym N,N′,N″-triarylguanidine in fair to good yield and the products have been characterized. Sym N,N′,N″-tri(4-tolyl)guanidine possesses (7) anti-anti conformation, sym N,N′,N″-tri(2-tolyl)guanidine (8) and sym N,N′,N″-tris(2,4-xylyl)guanidine (11) each possess anti-anti αβα conformation whereas sym N,N′,N″-tris(2-anisyl)guanidine possesses (9) syn-anti αββ conformation as determined by single crystal X-ray diffraction data. The observed conformations appear to result from a subtle balance between steric factor associated with the aryl substituent and multiple electronic factors namely n-π conjugation/negative hyperconjugation and non-covalent interactions in the crystal lattice.

The reactions of Zn(OAc)(2).2H(2)O with various positional isomers of lutidine were explored with a view to understand the factors responsible for the nuclearity/aggregation and acetate coordination modes of the products. The reactions of Zn(OAc)(2).2H(2)O with 3,5-lutidine, 2,3-lutidine, 2,4-lutidine, and 3,4-lutidine in a 1:1 ratio in methanol at ambient temperature afforded three discrete trinuclear complexes [Zn(3)(OAc)(2)(mu(2)-eta(2):eta(1)-OAc)(2)(mu(2)-eta(1):eta(1)-OAc)(2)(H(2)O)(2)(3,5-lutidine)(2)] (1), [Zn(3)(mu(2)-eta(1):eta(1)-OAc)(4)(mu(2)-eta(2):eta(0)-OAc)(2)L(2)] [L = 2,3-lutidine (2) and 2,4-lutidine (3)], and a one-dimensional coordination polymer [Zn(OAc)(mu(2)-eta(1):eta(1)-OAc)(3,4-lutidine)] (4) in 93, 79, 81, and 94% yields, respectively. Complexes 1-4 were characterized by microanalytical, IR, solution ((1)H and (13)C), and solid-state cross-polarization magic angle spinning (13)C NMR spectroscopic techniques and single-crystal X-ray diffraction data. Complex 1 is unique in that it contains three types of acetate coordination modes, namely, monodentate, bridging bidentate, and asymmetric chelating bridging. Variable-temperature (1)H NMR data indicated that complex 1 partially dissociates in solution, and the remaining undissociated 1 undergoes a rapid "carboxylate shift" even at 218 K. The plausible mechanism of formation of complexes 1-4 was explained with the aid of a point zero charge (pzc) model, according to which the nuclearity/aggregation observed in complexes 1-4 depends upon the number and nature of equilibrating species formed upon dissolution of the reactants in methanol, and these in turn depend upon the subtle basic/steric properties of lutidines. Further, noncovalent interactions play a crucial role in determining the nuclearity/aggregation and acetate coordination modes of the products.

N,N′,N′′-Tris(2-anisyl)guanidine, (ArNH)2CNAr (Ar = 2-(MeO)C6H4), was cyclopalladated with Pd(OC(O)R)2 (R = Me, CF3) in toluene at 70 °C to afford palladacycles [Pd{κ2(C,N)-C6H3(OMe)-3(NHC(NHAr)(NAr))-2}(μ-OC(O)R)]2 (R = Me (1a) and CF3 (1b)) in 87% and 95% yield, respectively. Palladacycle 1a was subjected to a metathetical reaction with LiBr in aqueous ethanol at 78 °C to afford palladacycle [Pd{κ2(C,N)-C6H3(OMe)-3(NHC(NHAr)(NAr))-2}(μ-Br)]2 (2) in 90% yield. Palladacycle 2 was subjected to a bridge-splitting reaction with Lewis bases in CH2Cl2 to afford the monomeric palladacycles [Pd{κ2(C,N)-C6H3(OMe)-3(NHC(NHAr)(NAr))-2}Br(L)] (L = 2,6-Me2C5H3N (3a), 2,4-Me2C5H3N (3b), 3,5-Me2C5H3N (3c), XyNC (Xy = 2,6-Me2C6H3; 4a), t BuNC (4b), and PPh3 (5)) in 87−95% yield. Palladacycle 2 upon reaction with 2 equiv of XyNC in CH2Cl2 afforded an unanticipated palladacycle, [Pd{κ2(C,N)-C(NXy)(C6H3(OMe)-4)-2(NC(NHAr)2)-3}Br(CNXy)] (6) in 93% yield, and the driving force for the formation of 6 was ascribed to a ring contraction followed by amine−imine tautomerization. Palladacycles 1a,b revealed a dimeric transoid in−in conformation with “open book” framework in the solid state. In solution, 1a exhibited a fluxional behavior ascribed to the six-membered “(C,N)Pd” ring inversion and partly dissociates to the pincer type and κ2-O,O′-OAc monomeric palladacycles by an anchimerically assisted acetate cleavage process as studied by variable-temperature 1H NMR data. Palladacycles 3a,b revealed a unique trans configuration around the palladium with lutidine being placed trans to the Pd−C bond, whereas cis stereochemistry was observed between the Pd−C bond and the Lewis base in 4a (as determined by X-ray diffraction data) and 5 (as determined by 31P and 13C NMR data). The aforementioned stereochemical difference was explained by invoking relative hardness/softness of the donor atoms around the palladium center. In solution, palladacycles 3a−c exist as a mixture of two interconverting boat conformers via a planar intermediate without any bond breaking due to the six-membered “(C,N)Pd” ring inversion, whereas palladacycles 4a,b and 5 exist as a single isomer, as deduced from detailed 1H NMR studies.

Simple routes to two new types of mononuclear cationic palladium phosphine acetate complexes featuring κ1- or κ2-carboxylates have been developed, and the resulting materials have been characterized by single-crystal X-ray diffraction. In acetonitrile the complex [(iPr3P)2Pd(κ2 O,O‘-OAc)]+ leads not to the independently prepared trans-[(iPr3P)2Pd(MeCN)(OAc)]+ but to reversible cyclometalation to form [(iPr3P)(MeCN)Pd(κ2 C,P-C(Me)2PiPr2)]+.

Reactivities of the dianionic guanidinate complex of [ i PrNdC(N i Pr) 2 ]Ta(NMe 2 ) 3 (1) and the monoanionic guanidinate complex Ta(NMe 2 ) 3 Cl[( i PrN) 2 CN(H) i Pr] (4) have been investigated. Reaction of 1 with Me 3 SiCl produced compound 2, Ta(NMe 2 ) 3 Cl[( i PrN) 2 CN-(SiMe 3 ) i Pr], which is proposed to arise from the addition of the Si-Cl bond across a Ta-N(guanidinate) bond of the starting material rather than one of the Ta-NMe 2 bonds. Complex 2 is the analogue of 4 in which H has been replaced by SiMe 3 . Derivatization of 2 was achieved by reaction with PhCH 2 MgCl to produce Ta(NMe 2 ) 3 (CH 2 Ph)[( i PrN) 2 CN-(SiMe 3 ) i Pr] (3). The single-crystal X-ray-determined structural features of 3 are reported and support the spectroscopic characterization of 3, and indirectly that of 2, by revealing a bidentate tetrasubstituted guanidinate monoanion and an η 1 -benzyl group. Complexes 1 and 4 insert 2,6-dimethylphenyl isocyanide (ArNC) to yield the structurally characterized complex Ta(NMe 5), which possesses one dianionic bidentate guanidinate ligand and two η 2 -iminocarbamoyl ligands derived from the insertion of ArNC into two of the Ta-NMe 2 bonds of the starting materials. The formally sevencoordinate Ta(V) center of 5 can be viewed as pseudo trigonal bipyramidal, with each of the η 2 -CdN linkages occupying a single coordination site. In the case of 4, the transformation of the guanidinate anion into its dianionic form was concomitant with insertion of ArNC. The sources of base for the deprotonation of the guanidinate ligand are likely the amido groups of a portion of the starting material.Supporting Information Available: Figures giving selected 1 H NMR spectra for 3 and X-ray diffraction data, including tables of atomic positions, thermal parameters, crystallographic data, and bond distances and angles and ORTEP drawings, for compounds 3 and 5. This material is available free of charge via the Internet at http://pubs.acs.org. OM991010F

Reaction of cis-[Cl(2)Pt(S(O)Me(2))(2)] with 1 equiv of sym-N,N',N″-triarylguanidines, ArN═C(NHAr)(2) (sym = symmetrical; Ar = 2-MeC(6)H(4) (LH(2)(2-tolyl)), 2-(MeO)C(6)H(4) (LH(2)(2-anisyl)), 4-MeC(6)H(4) (LH(2)(4-tolyl)), 2,5-Me(2)C(6)H(3) (LH(2)(2,5-xylyl)), and 2,6-Me(2)C(6)H(3) (LH(2)(2,6-xylyl))) in toluene under reflux condition for 3 h afforded cis- or trans-[Cl(2)Pt(S(O)Me(2))(ArN═C(NHAr)(2))] (Ar = 2-MeC(6)H(4) (1), 2-(MeO)C(6)H(4) (2), 4-MeC(6)H(4) (3), 2,5-Me(2)C(6)H(3) (4), and 2,6-Me(2)C(6)H(3) (5), respectively) in 83-96% yield. Reaction of cis-[Cl(2)Pt(S(O)Me(2))(2)] with 1 equiv of LH(2)(2-tolyl) and LH(2)(4-tolyl) in the presence of 1 equiv of NaOAc in methanol under reflux condition for 3 h afforded acetate-substituted products, cis-[(AcO)ClPt(S(O)Me(2))(ArN═C(NHAr)(2))] (Ar = 2-MeC(6)H(4) (6) and 4-MeC(6)H(4) (7)) in 83% and 84% yields, respectively. Reaction of cis-[Cl(2)Pt(S(O)Me(2))(2)] with 1 equiv of LH(2)(2-anisyl) and LH(2)(2-tolyl) in the presence of 1 equiv of NaOAc in methanol under reflux condition for 3 and 12 h afforded six-membered [C,N] platinacycles, [Pt{κ(2)(C,N)-C(6)H(3)R-3(NHC(NHAr)(═NAr))-2}Cl(S(O)Me(2))] (Ar = 2-RC(6)H(4); R = OMe (8) and Me (9)), in 92% and 79% yields, respectively. The new complexes have been characterized by analytical and spectroscopic techniques, and further the molecular structures of 1, 2, 4, 5, 6, and 8 have been determined by single-crystal X-ray diffraction. The platinum atom in 1, 4, and 5 exhibited the trans configuration, while that in 2, 6, and 8 exhibited the cis configuration. Complex 6 is shown to be the precursor for 9, and the former is suggested to transform to the latter possibly via an intramolecular C-H activation followed by elimination of AcOH. The solution behavior of new complexes has been studied by multinuclear NMR ((1)H, (195)Pt, and (13)C) spectroscopy. The new complexes exist exclusively as a single isomer (trans (1 and 5) and cis (6 and 7)), a mixture of cis and trans isomers with the former isomer being predominant in the case of 2 and the latter isomer being predominant in the case of 3. Complex 5 in the trans form revealed the presence of one isomer at 0.007 mM concentration and two isomers in about 1.00:0.12 ratio at 0.154 mM concentration as revealed by (1)H NMR spectroscopy, and this has been ascribed to the restricted Pt-S bond rotation at higher concentration. Platinacycle 8 exists as one isomer, while 9 exists as a mixture of seven isomers in solution. The influence of steric factor, π-acceptor property of the guanidine, subtle solid-state packing forces upon the configuration of the platinum atom, and the number of isomers in solution have been outlined. Factors that accelerate or slow down the cycloplatination reaction, the role of NaOAc, and a plausible mechanism of this reaction have been discussed.