This thesis reports on the reactions of alkylaluminium and gallium reagents with a number of different phosphorus acids, including substituted phosphates, phosphinic acids and phosphonic acids which afford dimeric metal phosphates [R₂M(O)₂P(OR')₂]₂ (M = Al, Ga; R = Me, Et, Pr, ⁱBu, Oc, OEt, Cl; R' - Et, Ph), dimeric metal phosphinates [R₂M(O)₂PR'₂]₂ (M = Al, Ga; R = Me, Et, Pr, ⁱBu, Oc, OEt, Cl; R' = Me, Ph, H) and tetrameric metal phosphonates [RM(O)₃PR']₄ (M = Al, Ga; R = Me, Et, ⁱBu, Cl; R' = Me, Et, Ph) respectively. All of these structures contain Al-O-P and Ga-O-P linkages as are found in the aluminophosphate and gallophosphate molecular sieves. The reactions of the alkylaluminium and alkylgallium reagents were found to give analogous products with the same degree of association. X-ray structures are reported for [Me₂Al(O)₂PPh₂]₂ and [Et₂Ga(O)₂PPh₂]₂ and show both products to be dimers containing puckered eight membered (M-O-P-O)₂ rings, which adopt chair conformations. EXAFS spectra were recorded for a number of the gallium compounds for which crystal structure could not be obtained. The EXAFS derived distances around the gallium centre in [Et₂Ga(O)₂PPh₂]₂ were found to be in good agreement with its crystal structure. The metal phosphonates, [RM(O)₃PR']₄, synthesised are the first examples of aluminium and gallium phosphonates reported. These were shown to be tetrameric by molecular weight measurements. A cube structure has been proposed for these compounds in which each face of the cube consists of an eight membered (M-O-P-O)₂ ring. Each metal or phosphorus atom forms a corner of the cube. The reactions of trialkylgallium reagents with the bulky phenols, 2,6-di-tert-buty-4-methylphenol and 2,6-diphenylphenol are described. The X-ray structure of (2,6-diphenyphenoxy)diethylgallium, [Et₂Ga(DPP)]₂ showed this compound to be dimeric with a core consisting of a four membered (Ga-O-Ga-O) ring.