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. 2014 Jun 15;760(100):74-83.
doi: 10.1016/j.jorganchem.2013.12.018.

A complete series of halocarbonyl molybdenum PNP pincer complexes - Unexpected differences between NH and NMe spacers

Sara Raquel M M de Aguiar  1 , Berthold Stöger  2 , Ernst Pittenauer  2 , Michael Puchberger  3 , Günter Allmaier  2 , Luis F Veiros  4 , Karl Kirchner  1
Affiliations

A complete series of halocarbonyl molybdenum PNP pincer complexes - Unexpected differences between NH and NMe spacers

Sara Raquel M M de Aguiar et al. J Organomet Chem. .

Abstract

In the present study a complete series of seven-coordinate neutral halocarbonyl Mo(II) complexes of the type [Mo(PNPMe-Ph)(CO)2X2] (X = I, Br, Cl, F), featuring the new PNP pincer ligand N,N'-bis(diphenylphosphino)-N,N'-methyl-2,6-diaminopyridine (PNPMe-Ph), were prepared and fully characterized. The synthesis of these complexes was accomplished by different methodologies depending on the halide ligands. For X = I and Br, [Mo(PNPMe-Ph)(CO)2I2] and [Mo(PNPMe-Ph)(CO)2Br2] were obtained by reacting [Mo(PNPMe-Ph)(CO)3] with stoichiometric amounts of I2 and Br2, respectively. Alternatively, these complexes were obtained upon treatment of [MoX2(CO)3(CH3CN)2] (X = I, Br) with 1 equiv. of PNPMe-Ph. On the other hand, in the case of X = Cl, [Mo(PNPMe-Ph)(CO)2Cl2] was afforded by the reaction of [Mo(CO)4(μ-Cl)Cl]2 with 1 equiv. of PNPMe-Ph. The equivalent procedure also worked for X = Br. Finally, addition of 1 equiv. of 1-fluoro-2,4,6-trimethylpyridinium tetrafluoroborate to [Mo(PNPMe-Ph)(CO)3] yielded the analogous fluorine complex [Mo(PNPMe-Ph)(CO)2F2]. The modification of the ligand scaffold by introducing a Me group instead of H changed the properties of the PNP-Ph ligand significantly. While in the present case exclusively neutral seven-coordinate complexes of the type [Mo(PNPMe-Ph)(CO)2X2] were obtained, with the parent PNP-Ph ligand, i.e., featuring NH spacers, cationic seven-coordinate complexes of the type [Mo(PNP-Ph)(CO)3X]X were afforded. DFT calculations indicated that the reactions are under thermodynamic control. The structures of representative complexes were determined by X-ray single crystal analyses.

Keywords: Carbon monoxide; DFT calculations; ESI mass spectrometry; Molybdenum complexes; PNP pincer ligands.

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Figures

None
Graphical abstract
Scheme 1
Scheme 1
Formation of cationic seven-coordinate halocarbonyl molybdenum complexes of the type [Mo(PNP)(CO)3X]+ (X = Cl, Br, I).
Fig. 1
Fig. 1
Structural view of [Mo(PNPMe-Ph)(CO)3]·CH2Cl2 (2·CH2Cl2) showing 50% thermal ellipsoids (hydrogen atoms and solvent omitted for clarity). Selected bond lengths (Å) and bond angles (°): Mo1-C32 2.020(1), Mo1-C331.957(1), Mo1-C34 2.030(1), Mo1-P1 2.3816(4), Mo1-P2 2.3890(4), Mo-N1 2.246(1), P1-Mo1-P2 155.48(1), N1-Mo1-C33176.22(5), C32-Mo1-C34166.15(5).
Scheme 2
Scheme 2
Formation of neutral seven-coordinate halocarbonyl molybdenum complexes of the type [Mo(PNP)(CO)2X2] (X = F, Cl, Br, I).
Scheme 3
Scheme 3
Synthesis of the fluoride complex [Mo(PNPMe–Ph)(CO)2F2] (3d).
Scheme 4
Scheme 4
Fragmentation pattern of [Mo(PNPMe–Ph)(CO)2X2] complexes observed in the ESI-MS experiments and the DFT calculated energy balance for X = Br.
Fig. 2
Fig. 2
Positive-ion ESI full scan mass spectrum of [Mo(PNPMe-Ph)(CO)2Br2](3b) (A) and corresponding MS/MS (low energy CID)-spectrum of in-source-generated [M + Na − CO]+ precursor ions (B). Inset shows the calculated and measured isotopic pattern of [M + Na − CO]+. In both spectra only signals containing the Mo-isotope of highest abundance (98Mo) are annotated.
Fig. 3
Fig. 3
(a) Structural view of [Mo(PNPMe-Ph)(CO)2l2]·CD2Cl2 (3a·CD2Cl2) showing 50% thermal ellipsoids (hydrogen atoms and solvent omitted for clarity). Selected bond lengths (Å) and bond angles (°): Mo1-l1 2.8888(5), Mo1-l22.8911(5), Mo1-P1 2.4364(7), Mo1-P2 2.4181(6), Mo-N1 2.276(2), Mo-C32 1.937(2), Mo-C33 1.991(2); P1-Mo1-P2 111.84(2), N1-Mo1-l1 94.11(4), N1-Mo1-l2 88.10(4), N1-Mo1-C32 122.64(7), N1-Mo1-C33 124.49(7), l1-Mo1-l2 82.27(1), C32-Mo1-C33 73.60(8).(b) Side view of 3a (hydrogen atoms, most phenyl carbon atoms, and solvent omitted for clarity).
Fig. 4
Fig. 4
(a) Structural view of [Mo(PNPMe-Ph)(CO)2Br2]·3CDCl3 (3b·3CDCl3) showing 50% thermal ellipsoids (hydrogen atoms and solvent molecules omitted for clarity). Selected bond lengths (Å) and bond angles (°): Mo1-Br1 2.6887(6), Mo1-Br22.6537(5), Mo1-P1 2.429(1), Mo1-P2 2.422(1), Mo-N1 2.249(3), Mo-C32 1.929(4), Mo-C33 2.016(4); P1-Mo1-P2 118.46(3), N1-Mo1-Br1 92.01(8), N1-Mo1-Br2 87.46(7), N1-Mo1-C32 120.5(2), N1-Mo1-C33 165.2(2), Br1-Mo1-Br2 80.56(2), C32-Mo1-C33 74.3(2).(b) Structural view of the inner coordination sphere of 3b emphasizing the trigonal monocapped antiprism with the C32-O1 ligand as capping ligand.
Fig. 5
Fig. 5
Structural view of [Mo(PNPMe-Ph)(CO)2Cl2]·1.5CD2Cl2 (3c·1.5CD2Cl2) showing 50% thermal ellipsoids (hydrogen atoms and solvent molecules omitted for clarity). Selected bond lengths (Å) and bond angles (°): Mo1-Cl1 2.5424(7), Mo1-Cl22.5031(8), Mo1-P1 2.4253(9), Mo1-P2 2.4259(8), Mo-N1 2.248(1), Mo-C32 1.950(2), Mo-C331.990(2); P1-Mo1-P2 120.18(2), N1-Mo1-Cl192.20(4), N1-Mo1-Cl2 86.96(3), N1-Mo1-C33117.00(6), N1-Mo1-C32169.96(6), Cl1-Mo1-Cl281.07(2), C32-Mo1-C3372.92(7).
Scheme 5
Scheme 5
Energy balance for the formation of complexes [Mo(PNP–Ph)(CO)3Br]Br and [Mo(PNP–Ph)(CO)2Br2].
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