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. 2013 May 24;32(10):3042-3052.
doi: 10.1021/om400254k. Epub 2013 May 7.

Synthesis and Characterization of Hydrido Carbonyl Molybdenum and Tungsten PNP Pincer Complexes

Ozgür Oztopcu  1 , Christian Holzhacker, Michael Puchberger, Matthias Weil, Kurt Mereiter, Luis F Veiros, Karl Kirchner
Affiliations

Synthesis and Characterization of Hydrido Carbonyl Molybdenum and Tungsten PNP Pincer Complexes

Ozgür Oztopcu et al. Organometallics. .

Abstract

In the present study the Mo(0) and W(0) complexes [M(PNP)(CO)3] as well as seven-coordinate cationic hydridocarbonyl Mo(II) and W(II) complexes of the type [M(PNP)(CO)3H]+, featuring PNP pincer ligands based on 2,6-diaminopyridine, have been prepared and fully characterized. The synthesis of Mo(0) complexes [Mo(PNP)(CO)3] was accomplished by treatment of [Mo(CO)3(CH3CN)3] with the respective PNP ligands. The analogous W(0) complexes were prepared by reduction of the bromocarbonyl complexes [W(PNP)(CO)3Br]+ with NaHg. These intermediates were obtained from the known dinuclear complex [W(CO)4(μ-Br)Br]2, prepared in situ from W(CO)6 and stoichiometric amounts of Br2. Addition of HBF4 to [M(PNP)(CO)3] resulted in clean protonation at the molybdenum and tungsten centers to generate the Mo(II) and W(II) hydride complexes [M(PNP)(CO)3H]+. The protonation is fully reversible, and upon addition of NEt3 as base the Mo(0) and W(0) complexes [M(PNP)(CO)3] are regenerated quantitatively. All heptacoordinate complexes exhibit fluxional behavior in solution. The mechanism of the dynamic process of the hydrido carbonyl complexes was investigated by means of DFT calculations, revealing that it occurs in a single step. The structures of representative complexes were determined by X-ray single-crystal analyses.

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Figures

Scheme 1
Scheme 1
Scheme 2
Scheme 2
Figure 1
Figure 1
Structural view of [W(PNP-Ph)(CO)3Br]Br·CH3OH (3a·CH3OH) showing 20% thermal ellipsoids (H atoms, Br– counterion, solvent molecule and subordinate Br/CO positions omitted for clarity). Selected bond lengths (Å) and bond angles (deg): W–C(31) = 2.017(5), W–C(30) = 2.020(6), W–C(32) = 2.024(8), W–N(1) = 2.237(3), W–P(1) = 2.4955(10), W–P(2) = 2.4895(11), W–Br(1) = 2.6015(5); P(1)–W–P(2) = 152.34(4), N(1)–W–P(1) = 77.44(9), N(1)–W–P(2) = 75.92(9), N(1)–W–C(30) = 137.76(16), N(1)–W–C(31) = 82.35(16), N(1)–W–C(32) = 150.87(8), N(1)–W–Br(1) = 82.28(9).
Figure 2
Figure 2
Structural view of [Mo(PNP-iPr)(CO)3Br]Br (4b) showing 50% thermal ellipsoids (Br– counterion omitted for clarity). Selected bond lengths (Å) and bond angles (deg): Mo–C(18) = 2.037(2), Mo–C(19) = 1.979(2), Mo–C(20) = 2.006(2), Mo–N(1) = 2.236(2), Mo–P(1) = 2.5242(5), Mo–P(2) = 2.5172(5), Mo–Br(1) = 2.6713(3); P(1)–Mo–P(2) = 150.80(2), N(1)–Mo–P(1) = 75.67(4), N(1)–Mo–P(2) = 75.35(4), N(1)–Mo–C(18) = 85.95(7), N(1)–Mo–C(19) = 77.73(6), N(1)–Mo–C(20) = 127.23(6), N(1)–Mo–Br(1) = 84.22(4).
Scheme 3
Scheme 3
Figure 3
Figure 3
Structural view of [Mo(PNPMe-iPr)(CO)3] (2d) showing 50% thermal ellipsoids (H atoms are omitted for clarity; the complex is mirror symmetric; symmetry code i for x, 1/2 – y, z). Selected bond lengths (Å) and bond angles (deg): Mo–C(14) = 1.956(2), Mo–C(15) = 2.0153(13), Mo–N(1) = 2.2589(15), Mo–P(1) = 2.3977(5), Mo–P(2) = 2.4070(5); P(1)–Mo–P(2) = 155.25(2), N(1)–Mo–P(1) = 77.74(4), N(1)–Mo–P(2) = 77.51(4), N(1)–Mo–C(15) = 98.52(4), C(15)–Mo–C(15i) = 162.93(7).
Figure 4
Figure 4
Structural view of [W(PNP-iPr)(CO)3]·THF·1/2C6H14 (5b·THF·1/2C6H14) showing 30% thermal ellipsoids (H atoms, solvent molecules, and alternative orientation of iPr group C(16a)–C(15a)–C(17a) omitted for clarity). Selected bond lengths (Å) and bond angles (deg): W–C(18) = 2.014(5), W–C(19) = 2.015(5), W–C(20) = 1.934(4), W–N(1) = 2.257(3), W–P(1) = 2.4080(12), W–P(2) = 2.4013(12); P(1)–W–P(2) = 154.43(4), N(1)–W–P(1) = 77.30(9), N(1)–W–P(2) = 77.18(9), N(1)–W–C(18) = 100.8(2), N(1)–W–C(19) = 93.3(2), N(1)–W–C(20) = 175.8(2), C(18)–W–C(19) = 165.7(2).
Figure 5
Figure 5
Structural view of [W(PNP-tBu)(CO)3]·THF (5c·THF) showing 50% thermal ellipsoids (H atoms and solvent molecule omitted for clarity). Selected bond lengths (Å) and bond angles (deg): W–C(22) = 1.941(3), W–C(23) = 1.997(2), W–C(24) = 2.001(2), W–N(1) = 2.277(2), W–P(1) = 2.4583(5), W–P(2) = 2.4656(5); P(1)–W–P(2) = 151.42(2), N(1)–W–P(1) = 76.52(4), N(1)–W–P(2) = 76.00(4), N(1)–W–C(22) = 169.53(8), N(1)–W–C(23) = 113.16(8), N(1)–W–C(24) = 90.27(7), C(23)–W–C(24) = 156.46(9).
Scheme 4
Scheme 4
Figure 6
Figure 6
Variable-temperature 300 MHz 1H NMR spectra of the hydride region of [Mo(PNP-Ph)(CO)3H]BF4 (7a) in CD2Cl2.
Figure 7
Figure 7
Structural view of [Mo(PNP-Ph)(CO)3H]BF4 (7a) showing 50% thermal ellipsoids (BF4– counterion and alternative orientation of C(32)–O(3) and H(1) omitted for clarity). Selected bond lengths (Å) and bond angles (deg): Mo–H(1) = 1.67(4), Mo–C(30) = 2.0368(15), Mo–C(31) = 2.0465(15), Mo–C(32) = 2.017(3), Mo–N(1) = 2.2357(11), Mo–P(1) = 2.4409(4), Mo–P(2) = 2.4489(4); P(1)–Mo–P(2) = 154.64(1), N(1)–Mo–P(1) = 77.39(3), N(1)–Mo–P(2) = 77.39(3), N(1)–Mo–C(30) = 87.62(5), N(1)–Mo–C(31) = 86.97(5), N(1)–Mo–C(32) = 163.73(9), N(1)–Mo–H(1) = 146.0(15), C(32)–Mo–H(1) = 50.2(15).
Figure 8
Figure 8
Structural view of [Mo(PNPMe-iPr)(CO)3H]BF4·CH2Cl2 (7d·CH2Cl2) showing 50% thermal ellipsoids (BF4– counterion and CH2Cl2 omitted for clarity). Selected bond lengths (Å) and bond angles (deg): Mo–H(1) = 1.63(2), Mo–C(20) = 2.0440(13), Mo–C(21) = 2.0239(13), Mo–C(22) = 1.9856(13), Mo–N(1) = 2.2462(10), Mo–P(1) = 2.4425(3), Mo–P(2) = 2.4776(3); P(1)–Mo–P(2) = 154.61(1), N(1)–Mo–P(1) = 77.29(3), N(1)–Mo–P(2) = 77.31(3), N(1)–Mo–C(20) = 94.27(4), N(1)–Mo–C(21) = 89.76(4), N(1)–Mo–C(22) = 162.26(4), N(1)–Mo–H(1) = 145.7(8), C(22)–Mo–H(1) = 52.0(8).
Figure 9
Figure 9
Structural view of [W(PNP-Ph)(CO)3H]BF4 (8a) showing 50% thermal ellipsoids (BF4– counterion and alternative orientation of C(32)–O(3) and H(1) omitted for clarity). Selected bond lengths (Å) and bond angles (deg): W–H(1) = 1.65(5), W–C(30) = 2.033(2), W–C(31) = 2.039(2), W–C(32) = 2.022(4), W–N(1) = 2.2316(15), W–P(1) = 2.4444(5), W–P(2) = 2.4459(5); P(1)–W–P(2) = 154.32(2), N(1)–W–P(1) = 77.17(4), N(1)–W–P(2) = 77.29(4), N(1)–W–C(30) = 87.78(7), N(1)–W–C(31) = 86.88(7), N(1)–W–C(32) = 162.35(11), N(1)–W–H(1) = 143.5(17), C(32)–W–H(1) = 53.9(17).
Figure 10
Figure 10
Free energy profile (in kcal/mol) for the “pseudorotation” of CO and hydride ligands in the complexes [M(PNP)(CO)3H]+ (M = W, Mo).
Figure 11
Figure 11
Front (left) and side views (right) of the optimized structures (DFT/B3LYP) of the tungsten complex [W(PNP-Ph)(CO)3H]+ (8a; top) and the transition state TS (bottom) with most phenyl carbon atoms and hydrogen atoms omitted for clarity.
Figure 12
Figure 12
Front (left) and side views (right) of the optimized structures (DFT/B3LYP) of the tungsten complex [W(PNP-tBu)(CO)3H]+ (8c; top) and the transition state TS (bottom) with most tBu carbon atoms and hydrogen atoms omitted for clarity.
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