Conformational Isomerism in Monomeric, Low‐Coordinate Group 12 Complexes Stabilized by a Naphthyl‐Substituted m‐Terphenyl Ligand

Abstract

The synthesis and characterization of the first series of low-coordinate bis(terphenyl) complexes of the Group 12 metals, [Zn(2,6-Naph2 C6 H3 )2 ] (1), [Cd(OEt2 )(2,6-Naph2 C6 H3 )2 ] (2) and [Hg(OEt2 )(2,6-Naph2 C6 H3 )2 ] (3) (Naph=1-C10 H7 ) are described. The naphthyl substituents of the terphenyl ligands confer considerable steric bulk, and as a result of limited flexibility introduce multiple conformations to these unusual systems. In the solid state, complex 1 features a two-coordinate Zn centre with the ligands oriented in a syn/anti conformation, whereas the three-coordinate distorted T-shaped complexes 2 and 3 feature the ligands in the syn/syn configurations. The results of DFT calculations are in good agreement with the solid-state configurations for these complexes and support the spectroscopic measurements, which indicate several conformers in solution.

Ligand influences on homoleptic Group 12 m-terphenyl complexes

“…(structure solution, structure refinement and molecular graphics). In the crystal structure of 1 a second twin component was detected: the twin law was (-1 0 0, 0 1 0, 0 0 -1) and the twin fraction refined to 0.336 (14). Merohedral crystal twinning [twin law (0 1 0, 1 0 0, 0 0 -1)] was detected for 2 and the twin fraction refined to 0.3834 (13).…”

“…where the cadmium and mercury diaryls are three-coordinate [(2,6-Naph 2 C 6 H 3 ) 2 M(OEt 2 ) (M = Cd, Hg)], 14 and is presumably due to the overall lower steric demands of the 1-naphthyl moiety compared to the 2,6-Xyl, 3,5-Xyl or Pmp substituents. Relevant bond lengths and angles for 1-3 can be found in Table 1, for 4-6 in Table 2 and for 7-9 in Table 3.…”

“…[13][14][15] We are interested in deducing how subtle changes in the steric pocket offered by the m-terphenyl ligands can affect the coordination environment around the metal centre, with the eventual aim to tailor the ligand sterics towards the investigation of bonding and small molecule reactivity.…”

Synthesis and structure of bis(m-terphenyl)zinc (2,6-Mes2 C6 H3)2 Zn

“…Differences are observed in the relative orientation of the phenyl rings. Like (C 6 F 5 ) 2 Zn (Sun et al, 1998), [6-(CF 3 )C 6 H 4 ] 2 Zn (Chisholm et al, 2005), the closely related (2,6-Naph 2 C 6 H 3 ) 2 Zn (Gridley et al, 2013), [2,6-(2,6-Xyl) 2 C 6 H 3 ] 2 Zn, [2,6-(3,5-Xyl) 2 C 6 H 3 ] 2 Zn, [2,6-Pmp 2 C 6 H 3 ] 2 Zn (Blundell et al, 2014) and the isoelectronic (2,6-Mes 2 C 6 H 3 ) 2 Hg (Niemeyer and Power, 1997), (2,6-Mes 2 C 6 H 3 ) 2 Zn adopts a nearly C s symmetry, while Mes 2 Zn (Cole et al, 2003;Krieck et al, 2009) and [3,5-(CF 3 ) 2 C 6 H 3 ] 2 Zn (Lai et al, 2012) possess a nearly C 2v symmetry. Presumably due to the large steric congestion, (2,4,6-t-Bu 3 C 6 H 2 ) 2 Zn (Westerhausen et al, 2005) and the related [2,4,6-(CF 3 ) 3 C 6 H 2 ] 2 Zn (Brooker et al, 1992) approach only C 2 symmetry.…”

Organic Transformations Catalysed by Low-Coordinate m-Terphenyl Complexes

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The use of sterically demanding m-terphenyl ligands allows the isolation of highly unsaturated transition metal complexes which show unusual bonding modes and reactivity [1,2,3,4]. In addition to stoichiometric reactivity towards small molecules, these complexes are efficient precatalysts for the cyclotrimerisation of isocyanates ( Figure 1); they exhibit high selectivity and allow the formation of mixed species through cross-coupling reactions [5].

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