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

[Display omitted] The influence of the weakly coordinating triflate anion is explored by reaction of M(OTf)3 (M = Al, Ga, In) with phosphine oxide and pyridine-N-oxide ligands, yielding a range of new complexes with κ1-coordinated and/or H-bonded triflate anions, the latter leading to formation of unusual complex anion motifs. 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, dppmO2 (Ph2P(O)CH2P(O)Ph2), with M(OTf)3 in a 3:1 ratio readily affords the tris-chelate species, [M(dppmO2)3][OTf]3 for all three metals, while a 2:1 ratio also gives [Ga(OTf)2(dppmO2)2][OTf]. Crystal structures of both [Al(dppmO2)3][OTf]3·MeCN and [Ga(dppmO2)3][OTf]3·2CHCl3 are reported. Multinuclear (1H, 13C{1H}, 19F{1H}, 31P{1H}, 27Al, 71Ga and 115In, where appropriate) NMR data show that in CD3CN the complexes are labile and the di