Functional groups are the cornerstone of predicting and rationalising reactivity in synthetic chemistry. The conceptual replacement of 2p elements in common functional groups with heavier main-group congeners can lead to drastically different properties and reactivity. The study of phosphorus-containing analogues of nitrogen-containing moieties has grown in recent years, with examples including phosphorus analogues of pyridine and urea (Figure ), as well as imines, nitriles, and the cyanate and cyanide anions. When phosphorus is in a low-coordinate environment, it has been shown that it is more similar to carbon than to nitrogen, principally due to the isolobal nature of P and C and their similar electronegativities, resulting in phosphorus being dubbed the carbon copy. For tri-coordinate phosphorus, the presence of the lone pair means that there are obvious parallels with analogous nitrogen compounds, although there is a significantly reduced propensity for delocalisation of this lone pair in the former. For example, in N,Ndimethylformamide (DMF), the nitrogen is planar and the methyl groups are inequivalent due to significant C-N double bond character, whereas in the heavier P,P-dimethylformylphosphine the phosphorus moiety is pyramidal and there is minimal donation of the lone pair into the C=O π* orbital (Figure ). Triazenes (RN=N-NR'2; Figure ) are a common functional group in organic chemistry, and can be found in dyes and pharmaceuticals, such as the anti-cancer medications Temozolomide and Dacarbazine. They are also versatile tools in organic synthesis, where the triazene moiety can act as a robust protecting group for amines, or as a precursor in numerous synthetic transformations. The literature on the coordination chemistry of neutral triazenes is scant. All examples feature monodentate coordination to the metal centre via the terminal imino nitrogen, and there are no examples of binding through the tri-coordinate amino nitrogen centre. N,N'-disubstituted triazenes are much more commonly deprotonated to afford anionic triazenides ([RNNNR] -), which can then act as monodenate, bidentate and bridging ligands to a wide range of metal centres. Triazenides are isoelectronic with amidinates ([RNC(R')NR] -), but the central electronegative nitrogen in triazenides results in a reduced charge density of the terminal nitrogen atoms relative to amidinates, which would confer an increased electrophilicity at the ligated metal centre. The conceptual replacement of the tri-coordinate nitrogen centre in triazenes with a phosphorus atom yields azophosphines: RN=N-PR'2 (Figure ). Azophosphines were first synthesised in the late 1970s by Wiberg and co-workers by the reaction of silyldiazenes and chlorophosphines, and alkenylsubstituted variants were subsequently prepared by Attanasi and co-workers. It was over 30 years later that this family of molecules were revisited, when Cummins and co-workers synthesised and crystallographically characterised MesN2PA (Mes = mesityl, A = anthracene, Scheme 1A). This molecule was prepared in 14% yield and was thermally unstable due to loss of the labile anthracene moiety, which enabled the molecule to act as a synthetic equivalent of mesitylphosphaazide (MesN2P) in a range of cycloaddition reactions. The Cummins group also recently published the synthesis of a wider family of azophosphines, and explored their reactivity with alkynes to afford Nheterocyclic iminophosphoranes. The azophosphines were synthesised in two different ways. The first method was analogous to Wiberg's approach involving the reaction of silyldiazenes and chlorophosphines, although this method was unsuccessful for sterically hindered chlorophosphines such as i Pr2PCl. The second approach involved oxidation of phosphinohydrazines with benzoquinones (BQ) and could tolerate the larger P-substituents i Pr and Cy (cyclohexyl), although the size of the BQ had to be tailored to the steric profile of the azophosphine (Scheme 1B). A general synthetic route to this family of compounds that tolerates bulky groups is still missing. This manuscript explores the synthesis and characterisation of a family of air-stable azophosphine-borane complexes, and their subsequent deprotection to the free azophosphines. These compounds are structurally characterised, both experimentally and computationally, and highlight the availability of the phosphorus lone pair for coordination. This is confirmed by demonstrating that neutral azophosphines can coordinate to a ruthenium(II) centre as both a mono-and bidentate ligand.