Unusual Reaction between (Nitrile)Pt Complexes and Pyrazoles:  Substitution Proceeds via Metal-Mediated Nitrile−Pyrazole Coupling Followed by Elimination of the Nitrile

Abstract

The reaction of platinum(IV) complex trans-[PtCl4(EtCN)2] with pyrazoles 3,5-RR'pzH (R/R' = H/H, Me/H, Me/Me) leads to the formation of the trans-[PtCl4{NH=C(Et)(3,5-RR'pz)}2] (1-3) species due to the metal-mediated nitrile-pyrazole coupling. Pyrazolylimino complexes 1-3 (i) completely convert to pyrazole complexes cis-[PtCl4(3,5-RR'pzH)2] by elimination of EtCN upon reflux in a CH2Cl2 solution or upon heating in the solid state; (ii) undergo exchange at the imino C atom with another pyrazole different from that contained in the pyrazolylimino ligand. The reaction of trans-[PtIICl2(EtCN)2] and 3,5-RR'pzH, conducted under conditions similar to those for trans-[PtIVCl4(EtCN)2], is much less selective, and the composition of the products strongly depends on the pyrazole employed: (a) with pzH, the reaction gives a mixture of three products, i.e., [PtCl2NH=C(Et)pz-kappa2N,N}] (4), [PtCl(pzH){NH=C(Et)pz-kappa2N,N}]Cl (5), and [Pt(pzH)2{NH=C(Et)pz-kappa2N,N}]Cl2 (6) (complexes 5 and 6 are rather unstable and gradually transform to trans-[PtCl2(pzH2] and [Pt(pzH)(4)]Cl(2) and free EtCN); (b) with 3,5-Me(2)pzH, the reaction leads to the formation of [PtCl2NH=C(Et)(3,5-Me2pz)-kappa2N,N}] (7) and [PtCl(3,5-Me2pzH)3]Cl (8); (c) in the case of asymmetric pyrazole 3(5)-MepzH, which can be added to EtCN and/or bind metal centers by any of the two nonequivalent nitrogen sites, a broad mixture of currently unidentified products is formed. The reduction of 1-3 with Ph3P=CHCO2Me in CHCl3 allows for the formation of corresponding platinum(II) compounds trans-[PtCl2{NH=C(Et)(3,5-RR'pz)}2] (9-11). Ligands NH=C(Et)(3,5-RR'pz) (12-14) were almost quantitatively liberated from 9-11 with 2 equiv of 1,2-bis-(diphenylphosphino)ethane in CDCl3, giving free imines 12-14 in solution and the precipitate of trans-[Pt(dppe)2](Cl)2. Pyrazolylimines 12-14 undergo splitting in CDCl3 solution at 20-25 degrees C for ca. 20 h to furnish the parent propiononitrile and the pyrazole 3,5-RR'pzH, but they can be synthetically utilized immediately after the liberation.

Dihalomethanes as Bent Bifunctional XB/XB‐Donating Building Blocks for Construction of Metal‐involving Halogen Bonded Hexagons

“…In two cases, hexagon-like moieties are not linked to the chains and stay as separated units (Figure S30, S32). [13] LICKAM CBr 4 0.86-0.87 [PtCl 2 (NCNEt 2 ) 2 ] [13] LICKIU CBr 4 0.92-0.98 [PdCl 2 (NCNMe 2 ) 2 ] [13] LIHMATC HBr 3 0.91 [PdCl 2 (NCNMe 2 ) 2 ] [13] LIHMEXC HI 3 0.89-0.90 [PtCl 2 (NCNMe 2 ) 2 ] [13] LIHMIBCHBr 3 0.92 [PtCl 2 (NCNCH(CH 2 ) 3 CH) 2 ] [20] UKAWOU CHI 3 0.87-0.89 [PtCl 2 (NCNMe 2 ) 2 ] [20] UKEKIG CHI 3 0.89-0.91 [PtBr 2 (NCNMe 2 ) 2 ] [20] UKELAZ CHI 3 0.89-0.90 [PtCl 2 (NCNEt 2 ) 2 ] [20] UKELEDC HI 3 0.87-0.94 [PPh 4 ][ReBr 4 (NO) 2 ] [21] BOJFOV CCl 4 0.95-0.99 [PdCl 2 (P(OC 12 H 8 O)OPh)] 2 [22] EJOHAN CHCl 3 0.97-0.99 [AsPh 4 ][W 2 Cl 2 (N 3 S 2 ) 3 ] [23] FEPVURCCl 4 0.98 [PtCl 2 (NHC(Et)(C 3 N 2 H 3 )] [24] MEHZAB CHCl 3 0.89-0.96 [SiBr 2 (OC(Ph)NHNC(Me) 2 ] [25] UFOYETCHCl 3 0.97-0.99 [NPr 4 ][CuBr 2 ] [26] HIGRAR CBr 4 0.85-0.91…”

Reactivity of Scorpionate-Anchored Yttrium Alkyl Complex toward Organic Nitriles

“…Organic nitrile is one useful reagent in organic synthesis for construction of many important N-heterocycle compounds, and its reactivity toward organometallic complexes is of fundamental interest in organometallic chemistry . The investigations on the reactivity of rare earth metal alkyl complexes toward organic nitriles provide many important organometallic reactions and interesting structures.…”

Metal-mediated coupling of a coordinated isocyanide and indazoles

“…It is important to mention that such a coupling is known for the isoelectronic nitrile RCN ligands and leads to the formation of imine complexes. 11,14 In order to verify the reactivity of the corresponding isocyanide species, we attempted to carry out the integration of an isocyanide in cis-[PdCl 2 (CNCy) 2 ] (1) with indazole (HInd, 2) or 5-methylindazole (HInd Me , 3), and report herein the first example of a metal-mediated addition of pyrrole type N-heterocycles to an isocyanide.…”