Abstract
The reaction between Mo(CO) <sub>2</sub> (CH <sub>3</sub> CN) <sub>2</sub> (η <sup>3</sup> -C <sub>5</sub> H <sub>7</sub> )Br and 2,2′-bipyridine (bpy) or 1,10-phenanthroline (phen) yields complexes of the type Mo(CO) <sub>2</sub> (N N)(η <sup>3</sup> -C <sub>5</sub> H <sub>7</sub> )Br (N N = bpy (1a), phen (1b)), respectively. Treatment of 1a or 1b with AgBF <sub>4</sub> in CH <sub>2</sub> Cl <sub>2</sub> respectively gives Mo(CO) <sub>2</sub> (N N)(η <sup>3</sup> -C <sub>5</sub> H <sub>7</sub> )BF <sub>4</sub> (N N = bpy (2a), phen (2b)), in which the pentadienyl ligand adopts a syn-η <sup>3</sup> configuration, whereas the BF <sub>4</sub> <sup>-</sup> anion serves as η <sup>1</sup> -coordinating ligand. In donor solvents such as CH <sub>3</sub> CN, THF, and acetone, 2a and 2b take up one solvent molecule to yield complexes of the type [Mo(CO) <sub>2</sub> (N N) (η <sup>3</sup> -C <sub>5</sub> H <sub>7</sub> )S]BF <sub>4</sub> (N N = bpy, S = CH <sub>3</sub> CN (3a), acetone (3b), ether (3c); N N = phen, S = CH <sub>3</sub> CN (4a), acetone (4b), ether (4c)). For 3a and 4a, two conformers are isolable in equal proportions. A <sup>1</sup> H spin saturation transfer experiment reveals that the two isomers undergo mutual exchange by rotation of the metal-allyl bond. For 3b,c, and 4b,c, one extra pair of conformers was detected in addition to the isomers identical with those of 3a and 4a. The 16-electron compound Mo(CO) <sub>2</sub> (N N) (η <sup>3</sup> -C <sub>5</sub> H <sub>7</sub> ) (5a; N N = (C <sub>6</sub> H <sub>5</sub> ) <sub>2</sub> B(pz) <sub>2</sub> , pz = pyrazolyl) has been synthesized from the reaction between NaB(C <sub>6</sub> H <sub>5</sub> ) <sub>2</sub> (pz) <sub>2</sub> and Mo(CO) <sub>2</sub> (CH <sub>3</sub> CN) <sub>2</sub> (η <sup>3</sup> -C <sub>5</sub> H <sub>7</sub> )Br. The solid-state structure of 5a has been fully characterized. In solution, the molecule is stereochemically nonrigid. There is NMR evidence that shows the chemical exchange between the two inequivalent pyrazole and the two inequivalent phenyl groups. The fluxional mechanism proceeds with rotation of the chelate nitrogen ligand along the Mo-B axis. Complex 5a reacts with tertiary phosphines to produce the 18-electron complexes Mo(CO) <sub>2</sub> (N N)(η <sup>3</sup> -C <sub>5</sub> H <sub>7</sub> )L (L = PMe <sub>3</sub> (6a), P(OPh) <sub>3</sub> (6b)). The reaction between H <sub>2</sub> O and 5a gives [(C <sub>6</sub> H <sub>5</sub> ) <sub>2</sub> B(pz)(OH)Mo(η <sup>3</sup> -NNCHCHCHCH <sub>2</sub> CHCHCHCH <sub>3</sub> )] (7a) in moderate yield. Structural characterization of 7a was achieved by X-ray diffraction studies of its tungsten analogue 7b. Molecular structures of 3a 5a, 6a, and 7b have been determined by X-ray diffraction with the following parameters: 3a, space group P1, α = 8.107 (4) Å, b = 11.055 (3) Å, c = 13.118 (3) Å, α = 106.42 (2)°, β = 95.39 (3)°, γ = 96.41 (3)°, R = 4.0% and R <sub>w</sub> = 4.1% for 2624 reflections >3.0σ(I); 5a, space group P1, a = 9.951 (13) Å, b = 10.435 (7) Å, c = 12.210 (8) Å, α = 82.31 (6)°, β = 79.27 (9)°, γ = 74.62 (10)°, R = 6.7%, and R <sub>w</sub> = 7.4% for 2368 reflections >2.0σ(I); 6a, space group P2 <sub>1</sub> /c, a = 14.552 (5) Å, b = 9.7108 (23) Å, c = 19.862 (8) Å, β = 90.48 (3)°. Z = 4, R = 4.2% and R <sub>w</sub> = 3.6% for 1421 reflections >2.0σ(I); 7b, space group P2 <sub>1</sub> 2 <sub>1</sub> 2 <sub>1</sub> , a = 10.0979 (21) Å, b = 13.6753 (23) Å, c = 17.331 (3) Å, Z = 4, R = 3.2% and R <sub>w</sub> = 2.7%, for 2650 reflections >2.0σ(I). © 1990 American Chemical Society.