Palladium Goes First: A Neutral Asymmetric HeteroditopicN,PLigand Forming Pd-3d Heterobimetallic Complexes

Abstract

A facile two-step synthesis of bis(1-methylhydrazinyl)pyrimidine from pyridine-2-carbaldehyde and 2diphenylphosphanylbenzaldehyde gave access to the new asymmetric ligand 1. The phosphane selectively guides Pd II into the softer tridentate N,N,P pocket, yielding monometallic complex 2. A second reaction with a 3d transition metal complex precursor (groups 7 to 12) fills the vacant N,N,N pocket and thus provides a variety of heterobimetallic complexes of the type Pd II /M II (M = Mn (3), Fe (4), Co (5), Ni (6), Cu (7), Zn ( 8)). Single-crystal X-ray diffraction studies were performed for all complexes. The assembly of μ 2 -chlorido-bridged dimers was observed for complexes 5−7 in the solid state, while DOSY NMR experiments have shown that 5−7 are unbridged monomers in solution. As an exception, Fe II prefers to form the homoleptic meridional complex [Fe{PdCl(1)} 2 ](OTf) 4 (4). The electrochemical behavior and the effective magnetic moment in solution were investigated for all complexes by cyclic voltammetry and Evans method, respectively. Experimental UV/vis results were interpreted by performing TD-DFT calculations on 1, 2, and 3.

Phosphorus guiding palladium: [4 + 4] metallomacrocyclic PdII complex and self-assembly of heterometallic PdII/ZnII grid-type complex

“…In previous studies, when the heteroditopic ligand 1 was reacted with [PdCl 2 (COD)] (COD = 1,5-cyclooctadiene) the preferred coordination of Pd II in the softer N,N,P pocket with selective formation of a monometallic Pd II complex [PdCl( 1 )]Cl was observed. 17 However, when [Pd(CH 3 CN) 4 ](OTf) 2 was employed featuring weakly coordinating triflate anions (OTf − = CF 3 SO 3 − ) instead of chloride, different complexes were obtained depending on the metal-to-ligand (M : L) ratio, 2 : 1 ( 2 ), 1 : 1 ( 3 ) and 1 : 2 ( 4 ) (Scheme 1). The homobimetallic complex 2 , in which the tridentate N,N,N as well as the N,N,P sites coordinate Pd II , was formed by addition of two equivalents of [Pd(CH 3 CN) 4 ](OTf) 2 to ligand 1 .…”

“…25 The synthesis and characterization of the ligand (1) have been previously reported. 17 All NMR spectra were recorded on a BRUKER Avance III HD 400 MHz NMR spectrometer at 25 °C ( 1 H 400.13 MHz, 13 C 100.63 MHz, 19 F 376.53 MHz and 31 P 162.02 MHz, two-dimensional ( 1 H-1 H COSY, 1 H-1 H NOESY, 1 H- 13 C HSQC, 1 H-13 C HMBC)). 1 H and 31 P{ 1 H} NMR spectra for compounds 4 and 7 have been measured at −5 °C.…”

“…In previous studies, when the heteroditopic ligand 1 was reacted with [PdCl 2 (COD)] (COD = 1,5-cyclooctadiene) the preferred coordination of Pd II in the softer N,N,P pocket with selective formation of a monometallic Pd II complex [PdCl(1)]Cl was observed. 17 Due to being involved in two five-membered chelate rings in the N,N,N pocket, Pd2 exhibits a more distorted square-planar geometry (τ 4 = 0.14) compared to Pd1 in the N,N,P coordination site (τ 4 = 0.10). 19 The intermetallic distance between Pd1 and Pd2 is 6.111(1) Å.…”

“…1,15,16 We have previously reported the synthesis of Pd II complexes based on the heteroditopic ligand 1 (Scheme 1) exhibiting a hard pyridine-hydrazone-pyrimidine (N,N,N) site and a softer pyrimidine-hydrazone-phosphane (N,N,P) pocket, in which Pd II is preferentially coordinated in the N,N,P pocket. 17 As the ligand coordinates Pd II in a tridentate fashion, the fourth coordination site of Pd II can be used for further modifications, for example, to form macrocyclic structures. Moreover, while the N,N,N pocket was previously used to synthesize homo-and heterobimetallic complexes, 17,18 we now report its use in the formation of heterometallic grid-type supramolecular structures.…”

“…17 As the ligand coordinates Pd II in a tridentate fashion, the fourth coordination site of Pd II can be used for further modifications, for example, to form macrocyclic structures. Moreover, while the N,N,N pocket was previously used to synthesize homo-and heterobimetallic complexes, 17,18 we now report its use in the formation of heterometallic grid-type supramolecular structures.…”