A Cyclometalated N‐Heterocyclic Carbene: The Wings of the First Pt₂(II,II) Butterfly Oxidized by CHI₃

Abstract

The X‐ray study on a single crystal of the butterfly‐like complex [{Pt(C^C*)(μ‐pz)}2] (1), containing a cyclometalated N‐heterocyclic carbene ligand as wings (HC^C*=1‐(4‐(ethoxycarbonyl)phenyl)‐3‐methyl‐1H‐imidazol‐2‐ylidene), showed three molecules in the asymmetric unit with intermetallic separations (Å) of 3.2294(4) (1A), 3.2834(4) (1B), and 3.1208(6) (1C). From the reaction of 1 with excess of CHI3 in the air and the sunlight, complex [{Pt(C^C*)(μ‐pz)I)}2] (2) (dPt−Pt=2.6079(2) Å) was obtained as the major product, while [IPt(C^C*)(μ‐pz)2Pt(C^C*)CHI2] (3) (dPt−Pt=2.6324(3) Å) was obtained as the major product under argon atmosphere in the dark. Experimental and theoretical investigations showed that an easily accessible radical‐like mechanism operates under thermal conditions, with dioxygen acting as an efficient radical (R.) scavenger. The oxidation of a Pt2(II,II) “butterfly” by CHI3 to give metal−metal bonded Pt2(III,III) compounds is described now for the first time.

Metal–Metal Cooperation in the Oxidation of a Flapping Platinum Butterfly by Haloforms: Experimental and Theoretical Evidence

“…In addition, the 1 H NMR spectra of 3-Cl/3-Br show a singlet corresponding to the Pt-CHX 2 fragment (6.59 ppm, 3-Cl; 6.05 ppm, 3-Br), which in the case of 3-Br displays the expected 195 Pt satellite pattern in accord with its dinuclear Pt 2 (III,III) formulation ( 2 J Pt,H = 24.4 Hz, 3 J Pt,H = 6.5 Hz) (Figure 1). These NMR features resembled those observed for [IPt- 25 and [Pt 2 (pop) 4 MeI] ( 1 J Pt,Pt = 1550 Hz). 30 The molecular structures of 2-Cl, 2-Br, and 3-Br, determined by single-crystal X-ray crystallography (see Figure 2 and the Supporting Information for a full description) were quite similar to those of [{Pt(C ∧ C*)(μ-pz)I)} 2 ] and [IPt-(C ∧ C*)(μ-pz) 2 Pt(C ∧ C*)CHI 2 ], respectively.…”

“…The starting material [{Pt(C ∧ C*)(μ-pz)} 2 ] (1) was prepared byfollowing the published procedure and isolated in a 1/9 syn/anti ratio. 25 Synthesis and Characterization of syn-/anti-[{Pt(EtO 2 C-C ∧ C*)(μ-pz)Cl)} 2 ] (2-Cl). Compound A (67.9 mg, 0.069 mmol) was allowed to react in CHCl 3 (15 mL) in ambient light at rt for 7.5 h. The resulting yellow solution was concentrated to ∼5 mL, and 10 mL of hexane was added to the residue to give 2-Cl-anti (96%)/ 2-Clsyn (4%) as a yellow solid.…”

“…30 The molecular structures of 2-Cl, 2-Br, and 3-Br, determined by single-crystal X-ray crystallography (see Figure 2 and the Supporting Information for a full description) were quite similar to those of [{Pt(C ∧ C*)(μ-pz)I)} 2 ] and [IPt-(C ∧ C*)(μ-pz) 2 Pt(C ∧ C*)CHI 2 ], respectively. 25 As far as we know, these are the only dinuclear metal−metal-bonded Pt III (μ-pz) 2 Pt III compounds reported to date.…”

“…16−23 In the course of our research we prepared the butterfly compound [{Pt(C ∧ C*)(μ-pz)} 2 ] (1) (HC ∧ C* = 1-(4-(ethoxycarbonyl)phenyl)-3-methyl-1H-imidazol-2-ylidene), and the reaction mechanism of 1 with CHI 3 was deeply studied. 25 To complete this piece of chemistry, we studied the reaction of 1 with CHCl 3 and CHBr 3 and the mechanisms of the thermal oxidation and photooxidation of 1 with CHBr 3 and CHCl 3 both experimentally and theoretically. Our results showed that the C ∧ C* basicity and the cooperative effects between the two adjacent metal centers in the Pt 2 (II,II) species are crucial to promote the C−X (X = Cl, Br) activation.…”

Bimetallic Platinum Group Complexes of a Macrocyclic Pyrazolate/NHC Hybrid Ligand

“…Instead, two resonances in the range between 140 and 150 ppm were observed, in which only one signal for the quaternary carbon of the pyrazolate moiety was expected. The resonance at 144.4 ppm was tentatively assigned to the carbene carbon based on the absence of 2/3 J Pt–C hyperfine coupling and 1 H, 13 C HMBC spectroscopy . However, no 1 J Pt–C coupling was detected, presumably due to the quadrupolar ( 14 N) nitrogen nuclei directly bound to the platinum centers, which also led to extensive 195 Pt NMR signal broadening ( W 1/2 = 136 Hz, see Supporting Information Figure S12).…”