A general route to monoorganopnicogen(III) (M = Sb, Bi) compounds with a pincer (N,C,N) group and oxo ligands

The reaction of RMCl2 [R = 2,6-[MeN(CH2CH2)(2)NCH2](2)C6H3; M = Sb (1), Bi (2)] with KOH affords the isolation of the oxides cyclo-R2M2O2 [M = Sb (3), Bi (4)]. Treatment of with trifluoroacetic acid produced an ionic species (5) with a dinuclear cation that contains organic ligands protonated partially at one of the pendant arms. The cyclic oxides 3 and 4 are able to trap gaseous CO2 to give RMCO3 [M = Sb (6), Bi (7)], the degree of these organometallic carbonates' oligomerization being under investigation. The reactivity of the dinuclear oxide 3 was also investigated towards oxalic acid or dopamine hydrochloride and pure mononuclear compounds could be isolated, i.e. RSb[O(O)CC(O)O] (8) and RSb[O-2-1,2-C6H3-3-(CH2)(2)NH3]Cl (9). The reaction of the dichlorides 1 and 2 with ethylene glycol, pinacol or catechol, in the presence of KOH, led to 2-organo-1,3,2-dioxastibolanes or - bismolanes RM(OCH2)(2) [M = Sb (10), Bi (11)], RM(OCMe2)(2) [M = Sb (12), Bi (13)] and 2-organo-1,3,2-dioxastibole or -bismole RM(O-2-1,2-C6H4) [M = Sb (14), Bi (15)], respectively. The compounds were investigated by NMR spectroscopy, including variable temperature experiments, providing evidence for the presence of the intramolecular N -> M interactions in solution. Single crystal X-ray diffraction studies were performed for most compounds and revealed an organic group R acting as a pincer ligand resulting in a distorted square pyramidal (N,C,N)MO2 core with cis intramolecular N -> M interactions placed trans to M-O bonds. This is in contrast to the N -> M interactions trans to each other as found in the RMCl2 used as starting materials. The crystals of the oxides 3 and 4.4H(2)O contain different geometric isomers with anti and syn orientation of the M-C bonds, respectively, with respect to the planar M2O2 ring. In the supramolecular polymeric architecture established in the crystal of 4.4H(2)O an important finding is the experimental observation of water hexamer units with a [tetramer + 2] structure (water molecules connected to opposite corners of a square water tetramer) fixed between 1D-chains of the type (syn-R2Bi2O2 center dot H2O)n through additional hydrogen bonds to oxygen atoms of the dinuclear organobismuth(iii) moieties. Theoretical calculations were carried out on 2-6 and 8-15 in order to gain insight into the stabilization energy produced by intramolecular coordination of the pendant arms, association degrees and formation energies of the organopnicogen compounds with chelating ligands.