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Cyclenphosphorane reacts with diborane at 0 °C to afford bis(borane)cyclenphosphorane, (C8H17N4P)(BH3)2 (2), in close to quantitative yield. No evidence for the formation of an adduct of the open-form tautomer, as from cyclamphosphorane, was found. 2 provides the first example of a stable H3B-N-P-N-BH3 sequence (dec 200 °C). It crystallizes in the orthorhombic space group P2{2{2X with a = 6.217 (2) Á, b = 12.557 (4) Á, c = 16.519 (6) Á, and Z = 4. The arrangement of the five bonds around phosphorus is close to that of a regular trigonal bipyramid (displaced 10.4% from the idealized trigonal bipyramid toward the square pyramid). Both BH3 groups are coordinated to apical nitrogen atoms, but the B-N bonds do not lie in the same plane, which implies a slightly helical distortion of the molecule. The apical P-N bonds (1.872 (5), 1.864 (5) Á) are the longest reported for a phosphorane, and it is proposed that each of them is a single apical P(V)-N(III) bond. Among the derivatives of cyclenphosphorane whose structure is known, 2 also has the shortest equatorial P-N bonds (1.645 (5), 1.654

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