Chemistry of coordinated nitroxyl. Reagent-specific protonations of trans-Re(CO)(2)(NO)(PR3)(2) (R = Ph, Cy) that give the neutral nitroxyl complexescis,trans-ReCl(CO)(2)(NH=O)(PR3)(2) or the cationic hydride complex [trans,trans-ReH(CO)(2)(NO)(PPh3)(2)(+)][SO3CF3-]

The reactions of hydrochloric and triflic acids with the five-coordinate ni trosyl complexes trans-Re(CO)(2)(NO)(PR3)2 (2a, R = Ph; 2b, R = Cy) have be en investigated. Reaction of anhydrous HCl with 2 results in a formal proto nation of the nitrosyl ligand and addition of chloride to the metal, giving the neutral nitroxyl complex cis,trans-ReCl(CO)(2)(NH=O)(PR3)(2) (3a, R = Ph; 3b, R = Cy). Reaction of Bronsted bases with 3a or 3b results in clean conversion of 3 to 2 when the base is appropriately strong (pK(b) approxima te to 7). Addition of HOSO2CF3 to solutions of 2a results in protonation at the metal and formation of the cationic rhenium hydride [trans, trans-ReH( CO)(2)(NO)(PPh3)(2)(+)][SO3CF3-] (4) in 74% yield; the deuteride [trans, tr ans-Re(H-2)(CO)(2)(NO)(PPh3)(2)(+)][SO3CF3-] (4-d) was analogously prepared from (HOSO2CF3)-H-2. 4 crystallized from CH2Cl2/Et2O solution in the ortho rhombic space group Pnma, with a = 17.2201(2) Angstrom, b = 23.6119(3) Angs trom, c = 9.2380(2) Angstrom, and Z = 4. The least-squares refinement conve rged to R(F) = 0.039 and R(wF(2)) = 0.063 for the 4330 unique data with I > 2 sigma (I). The structure of 4 shows that the hydride (Re-H = 1.74 A Angs trom occupies the position trans to the linear nitrosyl ligand (Re-N-O = 17 8.1(4)degrees) in the pseudooctahedral complex cation. Complex 4 does not r eact with chloride to give 3a. DFT calculations carried out on free nitroxy l and its model complexes [Re(CO)(5)(NH=O)(+)] (5), [mer,trans-Re(CO)(3)(NH =O)(PH3)(2)(+)] (6), and cis,trans-ReCl(CO)(2)(NH=O)(PH3)(2) (7) indicate t hat coordinated nitroxyl acts as both a a-donor and T-acceptor ligand, cons istent with the observed trend for v(NO) in free HN=O (1563 cm(-1)), [mer,t rans-Re(CO)(3)(NH=O)(PPh3)(2)(+)] (1, 1391 cm(-1)), 3a (1376 cm(-1)), and 3 b (1335 cm(-1)).