Synthesis, Reactivity, Structural Aspects, and Solution Dynamics of Cyclopalladated Compounds of N,N′,N′′-Tris(2-anisyl)guanidine

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), tBuNC (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.