3341tution has a similar but smaller effect upon nitrogen protonation.A computer fit of the NMR chemical shift vs pH curves allowed the intrinsic shifts of the various ligand protonated species, H,L, to be obtained. The 31P shifts for the various H,L species are dependent upon protonation of the nitrogen and the phosphonatt oxygen atoms, and also on the possible formation of intramolecular hydrogen bonds between NH+ and 0-neighboring groups. Those effects are reflected in the 31P chemical shifts in a complex way through u and ?r contributions to the electronic structure of the phosphonate moiety.44 The protonation shifts of the phosphonate ligands were used to obtain microscopic protonation fractions at various pH values. Although a quantitative fit of the experimental data was difficult due to pH-dependent conformational effects, the general picture of microscopic protonation of the macrocyclic phosphonate ligands is not very different from that found for the acetate c o~t e r p a r t s .~~-~~ The most basic sites are two ring nitrogens, followed by the phosphonate oxygens, which are protonated to different degrees depending on the ring structure. In the tetraaza ligand, the protonation of the pendant phosphonate oxygens is more extensive than in the triaza ligand before further protonation of the ring nitrogens occurs. Finally, the magnitude and sign of the Na+-induced shift on the IH and 31P signals of the phosphonate chelates indicate that this ion binds within the macrocyclic cavities of NOTP and DOTP but not DOTRP, at least below pH 13. This may be due to an unusually high first protonation constant for DOTRP or to unique conformational features of the bridging propylenes in this chelate that precludes Na+ binding in its cavity.
Acknowledgment.The reactions of RzPNMe2, Me2PNR'2, and (Me2N),PMe3-,, where R = Me, Et, Ph, and CI, R' = Me, Et, PP, Pr', and SiMe3, and n = 1-3, with varying mole ratios of BH3.THF have been carried out and studied by using multinuclear NMR spectroscopy. Although P-B-bonded monoadducts were always obtained, B-P-N-B-bonded bisadducts were also obtained for Me2PNMez, Me2PNEt2, and EtzPNMe2. These are the first reported examples where the nitrogen atom in acyclic aminophosphines demonstrates reactivity toward BH3. The extent of bisadduct formation decreases dramatically in going from MqPNMe, to MqPNEtp Kq, AH, and A S values were obtained for the MezPNMe2.BH3/H3BP(NMe2-BH3)Me2 and Et2PNMe2.BH3/H3BP(NMez* BH3)Et2 equilibrium systems. The results are compared with those reported previously for analogous aminoarsines. A competition study involving the Me3N, Me3P, Me3As, Me2PNMez, MezAsNMez, and BH3.THF systems is discussed relative to the nature of P-N and As-N bonding.