Considering that nitrous oxide and many other small molecules have already been reported to form complexes with frustrated Lewis pairs (FLPs), we added tris(pentafluorophenyl)borane (B(C6F5)3, BCF) to a solution of Cy3P=NP(O)A in dichloromethane, leading to new P NMR resonances at δ 52.5 and δ 32.9 ( 2 JPP = 16.8 Hz) in the 31 P{ 1 H} NMR spectrum (Figure ). After the reaction mixture stirred for 30 min at room temperature, all volatile materials were removed under reduced pressure, allowing us to isolate Cy3P-NP(A)O-B(C6F5)3 as a colorless solid in quantitative yield (Figure ). An analytical sample was crystallized in diethyl ether and the crystals were analyzed in a X-ray diffraction experiment, leading to the structure depicted in Figure . For the complete complexation of NPO, A can be cleaved off by irradiating (λ = 254 nm) a solution of Cy3P-NP(A)O-B(C6F5)3 in benzene or toluene for 220 min. Anthracene photodimerizes during the irradiation and can separated from the reaction mixture by filtration. The slightly yellow colored filtrate was mixed (in the case of benzene as a solvent) or layered with pentane and placed in the freezer. After three days colorless crystals formed and the crystals were collected by vacuum filtration, washed with pentane and isolated in 42% yield (Figure ). When the isolated material was dissolved in chloroform a doublet signal at δ 44.1 (J = 78.2 Hz) for PCy3 and a doublet of quintets signal at δ 271.1 ppm (J = 77.4, 25.5 Hz) for NPO were observed in the 31 P{ 1 H} NMR spectrum (Figure ). X-ray diffraction analysis on a single crystal directly grown from a benzene/pentane solution after irradiation reveals the Cy3P-NPO-B(C6F5)3 structure (Figure ). The latter splitting originates from through space coupling of phosphorus to fluorine in B(C6F5)3 as only a doublet signal is observed in the 31 P{ 1 H, F} NMR experiment. The compound is thermally unstable and decomposes after one day at room temperature or by heating over night at 50 °C. In the 31 P{ 1 H} NMR spectrum, two major doublet signals at δ 42.2 and δ 40.7 ppm together with some minor signals at around δ -20 ppm were observed that could not be unambiguously assigned (Figure ). The interatomic distances in the single crystal for the NPO fragment are almost the same for the N-P (1.5555(9) Å) and P-O (1.5549(8) Å) linkages. Intrinsic Bond Orbital (IBO) analysis shows the bonding of the π system, where there is visual evidence for both N-P and P-O π bonding (Figure ). The Wiberg bond order (WBO) for the N-P bond is 1.47 and for the P-O bond 1.05. The bond orders are reflective of the high electronegativity of N and O and the consequent greater coefficients on N and O rather than P in the π system, which acts to bring down the WBO numbers. Hence, the main resonance contributor is the one with the Cy3P ⊕ -N=P-O-B ⊖ (C6F5)3 bonding pattern, and formal positive and negative charges on the phosphine and borate, respectively. Compounds of the type R-N=P-OR' exhibit a similar bonding pattern, but they are rare and mainly derive from the combination of an alkoxide with the Mes*NP+ cation. Gaseous NPO is predicted to be linear, and has two bonds of almost equal length, a N-P bond distance of 1.4965Å at the CCSD(T)/CBS level and a P-O bond distance of 1.4656Å at the same level. Similar to N2O, the geometry of NPO is bent in its FLP complex.