Depending on the electrophilic reagent RX, the substitution reactions of Li(cyclen)P afford both the "open" N-R bonded species R(cyclen)P as well as the "closed" P-R bonded species (cyclen)PR. With Mes(2)BF or Ph(2)PCl, the open products Mes(2)B(cyclen)P and Ph(2)P(cyclen)P are formed. With MeCl, a mixture of both (cyclen)PMe and Me(cyclen)P are produced, with the former being the primary product. The X-ray crystal structure of Mes(2)B(cyclen)P was obtained and reveals that there is no interaction between the (boron-bound) nitrogen and the phosphorus, while the B-N bond length of 1.407(5) Angstrom indicates significant pi-bonding. These data suggest that larger substituents capable of pi-bonding favor the open isomer. Crystal data : Pbca, orthorhombic, a 12.083 (3) Angstrom, b = 13.447 (3) Angstrom, 30.533 (7) Angstrom, Z = 8.