Mono- and di-phosphine oxide complexes of aluminium, gallium and indium with weakly coordinating triflate anions-Synthesis, structures and properties

Reaction of the Group 13 triflates, M(OTf)(3) (M = Al, Ga, In; OTf = CF3SO3-), with 3 mol. eq. of R3PO (R = Ph or Me) gives the six-coordinate complexes, [M(OTf)(3)(R3PO)(3)], with coordinated triflate, as white powdered solids. Similarly, using 3 mol. eq. of PyNO (pyridine-N-oxide) readily forms [In(OTf)(3)(PyNO)(3)], whose crystal structure confirms a mer octahedral arrangement. In contrast, reaction of the harder Lewis acids Al(III) and Ga(III) with PyNO produce mixtures, mostly likely of the 3:1 and 4:1 species, [M(OTf)(3)(PyNO)(3)] and [M(OTf)(2)(PyNO)(4)][OTf] (M = Al, Ga). Both of the tetrakis species have been confirmed via single crystal X-ray studies and shown to exist as trans isomers. Higher ratios (4:1, 5:1 and 6:1) of Me3PO coordinated to In(OTf)(3) can also be achieved by varying the reaction stoichiometry appropriately, with the coordinated OTf groups readily displaced by the Me3PO. Crystal structures of two polymorphs of the salt, [In(OTf)(2)(Me3PO)(4)][In{(OH2)(2)(OTf)(4)}(Me3PO)(4)], in which the [In{(OH2)(2)(OTf)(4)}(Me3PO)(4)](-) anion is (unusually) comprised of a 'InIII(OH2)(2)(Me3PO)(4)' unit with four OTf anions H-bonded to the aquo ligands, giving the overall monoanionic charge. A similar arrangement is present in [In(OTf)(2)(Ph3PO)(4)][In{(OH2)(4)(OTf)(4)}(Ph3PO)(2)], the structure of which shows that all of the H atoms associated with the four aquo ligands in the [In{(OH2)(4)(OTf)(4)}(Ph3PO)(2)](-) form significant H-bonds to the OTf groups; specifically, the four OTf- anions each show two O...H interactions, forming bridges that link the equatorial aquo ligands into a 24-membered 'pseudo-macrocyclic' ring. The crystal structure of the mononuclear 5:1 complex, [Ga(Me3PO)(5)(MeCN)][OTf](3), is also described. Using the diphosphine dioxide, dppmO(2) (Ph2P(O)CH2P(O)Ph-2), with M(OTf)(3) in a 3:1 ratio readily affords the tris-chelate species, [M(dppmO(2))(3)][OTf](3) for all three metals, while a 2:1 ratio also gives [Ga(OTf)(2)(dppmO(2))(2)] [OTf]. Crystal structures of both [Al(dppmO(2))(3)][OTf](3).MeCN and [Ga(dppmO(2))(3)][OTf](3).2CHCl(3) are reported. Multinuclear (H-1,C-13{H-1}, F-19{H-1}, P-31{H-1}, Al-27, Ga-71 and In-115, where appropriate) NMR data show that in CD3CN the complexes are labile and the different R3PO coordination environments are not distinguished (although exchange between coordinated and 'free' Me3PO is slow on the P-31 NMR timescale), while the MeCN solvent also replaces OTf in the metal coordination sphere.

Automated summary

The reaction of Group 13 triflates with various ligands results in the formation of diverse complexes, some of which have unique structures as confirmed by crystallography analysis, highlighting the coordination environment of the ligands with the metal ions.