Transition metal pyridine complexes

Transition metal pyridine complexes encompas many coordination complexess that contain pyridine as a ligand. Most examples are mixed-ligand complexes. Many variants of pyridine are also known to coordinate to metal ions, such as the methylpyridines, quinolines, and more complex rings.

Structure of [Ru(NH3)5py]2+, illustrating the steric avoidance of the 2,6-protons and the cis ligands.[1]

Bonding

With a pKa of 5.25 for its conjugate acid, pyridine is about 15x less basic than imidazole. Pyridine is a weak pi-acceptor ligand. Trends in the M-N distances for complexes of the type MCl2(py)4]2+ reveal an anticorrelation with d-electron count.[2] Few low-valent metal complexes of pyridines are known. The role of pyridine as a Lewis base extends also to main group chemistry. Examples include sulfur trioxide pyridine complex SO3(py) and pyridine adduct of borane, BH3py.

Octahedral complexes
trans-[MCl2(pyridine)4]n+ is a common type of transition metal pyridine complex.
Chloro(pyridine)cobaloxime.

Owing to the relatively wide C-N-C angle, the 2,6-hydrogen atoms interfere with the adjacent ligands. Consequently, relatively few octahedral homoleptic pyridine complexes are known. These include [Ru(py)6]2+.[3] and .[4] Far more common are complexes of the type [MCl2(py)4]n+, which are invariably trans. Other common classes of complexes are the tris(pyridine) trihalides [MCl3(py)3] (M = Ti, Cr, Rh, Ir).

MCl2(pyridine)4 complexes
formulaCAS RNdensity from X-ray (g/cm3)
TiCl2(pyridine)4131618-68-31.383[5]
VCl2(pyridine)4[6]15225-42-01.346[7]
CrCl2(pyridine)4.acetone51266-53-61.383[8]
MnCl2(pyridine)414638-48-31.383[9]
FeCl2(pyridine)415138-92-81.383[2]
CoCl2(pyridine)413985-87-01.383[2]
NiCl2(pyridine)414076-99-41.383[2]
[RhCl2(pyridine)4]+14077-30-6 (Cl- salt)
RuCl2(pyridine)416997-43-61.549[10]
[MoX2py)4]+isolated as the salt with [MoX4py2]-[11]
NbCl2(pyridine)4168701-43-71.528[12]

Four-coordinate complexes
Collins reagent, the complex CrO3(pyridine)2, is a reagent in organic chemistry.[13]

Four-coordinate complexes include tetrahedral and square planar derivatives. Examples of homoleptic tetrahedral complexes include [M(py)4]n+ for Mn+ = Cu+,[14] M = Ni2+[15], Ag+.[16] Examples of homoleptic square planar complexes include the d8 cations [M(py)4]n+ for Mn+ = Pd2+,[17] Pt2+,[18] Au3+.[19]

Two-coordinate complexes

Examples include the homoleptic complexes of d10 metal centers. Examples include [M(py)2]+ (M = Cu, Ag, Au), which form colorless, diamagnetic salts.[19]

Applications and occurrence

Transition metal pyridine complexes have few practical applications, but they are widely used precursors to varioous homogeneous catalysts.[20] Crabtree's catalyst, a popular catalyst for hydrogenations, is a pyridine complex.

Unlike imidazoles, pyridine and its derivatives are uncommon ligands in nature.

References
  1. Shin, Yeung-gyo K.; Szalda, David J.; Brunschwig, Bruce S.; Creutz, Carol; Sutin, Norman (1997). "Electronic and Molecular Structures of Pentaammineruthenium Pyridine and Benzonitrile Complexes as a Function of Oxidation State". Inorganic Chemistry. 36 (14): 3190–3197. doi:10.1021/ic9700967. PMID 11669976.
  2. Long, Gary J.; Clarke, Peter J. (1978). "Crystal and molecular structures of trans-tetrakis(pyridine)dichloroiron(II), -nickel(II), and -cobalt(II) and trans-tetrakis(pyridine)dichloroiron(II) monohydrate". Inorganic Chemistry. 17 (6): 1394–1401. doi:10.1021/ic50184a002.
  3. Templeton, Joseph L. (1979). "Hexakis(pyridine)ruthenium(II) tetrafluoroborate. Molecular structure and spectroscopic properties". Journal of the American Chemical Society. 101 (17): 4906–4917. doi:10.1021/ja00511a020.
  4. Lichtenberg, Crispin; Adelhardt, Mario; Wörle, Michael; Büttner, Torsten; Meyer, Karsten; Grützmacher, Hansjörg (2015). "Mono- and Dinuclear Neutral and Cationic Iron(II) Compounds Supported by an Amidinato-diolefin Ligand: Characterization and Catalytic Application". Organometallics. 34 (12): 3079–3089. doi:10.1021/acs.organomet.5b00395.
  5. Wijeratne, Gayan B.; Zolnhofer, Eva M.; Fortier, Skye; Grant, Lauren N.; Carroll, Patrick J.; Chen, Chun-Hsing; Meyer, Karsten; Krzystek, J.; Ozarowski, Andrew; Jackson, Timothy A.; Mindiola, Daniel J.; Telser, Joshua (2015). "Electronic Structure and Reactivity of a Well-Defined Mononuclear Complex of Ti(II)". Inorganic Chemistry. 54 (21): 10380–10397. doi:10.1021/acs.inorgchem.5b01796. PMID 26451744.
  6. Edema, Jilles J. H.; Stauthamer, Walter; Van Bolhuis, Fre; Gambarotta, Sandro; Smeets, Wilberth J. J.; Spek, Anthony L. (1990). "Novel vanadium(II) amine complexes: A facile entry in the chemistry of divalent vanadium. Synthesis and characterization of mononuclear L4VCl2 [L = amine, pyridine]: X-ray structures of trans-(TMEDA)2VCl2 [TMEDA = N,N,N',N'-tetramethylethylenediamine] and trans-Mz2V(py)2 [Mz = o-C6H4CH2N(CH3)2, py = pyridine]". Inorganic Chemistry. 29 (7): 1302–1306. doi:10.1021/ic00332a003.
  7. D.J.Brauer, C.Kruger (1973). Cryst.Struct.Commun. 2: 421. Missing or empty |title= (help)CS1 maint: uses authors parameter (link)
  8. Cotton, F.Albert; Daniels, Lee M.; Feng, Xuejun; Maloney, David J.; Murillo, Carlos A.; Zúñiga, Luis A. (1995). "Experimental and theoretical study of a paradigm Jahn-Teller molecule, all-trans-CrCl2(H2O)2(pyridine)2, and the related trans-CrCl2(pyridine)4·acetone". Inorganica Chimica Acta. 235 (1–2): 21–28. doi:10.1016/0020-1693(95)90041-4.
  9. Wijeratne, Gayan B.; Zolnhofer, Eva M.; Fortier, Skye; Grant, Lauren N.; Carroll, Patrick J.; Chen, Chun-Hsing; Meyer, Karsten; Krzystek, J.; Ozarowski, Andrew; Jackson, Timothy A.; Mindiola, Daniel J.; Telser, Joshua (2015). "Electronic Structure and Reactivity of a Well-Defined Mononuclear Complex of Ti(II)". Inorganic Chemistry. 54 (21): 10380–10397. doi:10.1021/acs.inorgchem.5b01796. PMID 26451744.
  10. Wong, W. T.; Lau, T. C. (1994). "Trans-Dichlorotetrapyridineruthenium(II)". Acta Crystallographica Section C Crystal Structure Communications. 50 (9): 1406–1407. doi:10.1107/S0108270194002088. hdl:10722/69086.
  11. Brenčič, J. V.; Golič, L.; Leban, I.; Rotar, R.; Sieler, J. (1996). "Synthesis oftrans,trans-[MoX2py4][MoX4py2],trans-[MoX2py4]Br3, and structural identification oftrans,trans-[MoX2py4][MoX4py2] (X = Cl, Br; py = pyridine)". Zeitschrift fuer Anorganische und Allgemeine Chemie. 622 (12): 2124–2128. doi:10.1002/zaac.19966221222.
  12. Araya, Miguel A.; Cotton, F. Albert; Matonic, John H.; Murillo, Carlos A. (1995). "An Efficient Reduction Process Leading to Titanium(II) and Niobium(II): Preparation and Structural Characterization of trans-MCl2(py)4 Compounds, M = Ti, Nb, and Mn". Inorganic Chemistry. 34 (22): 5424–5428. doi:10.1021/ic00126a009.
  13. J. C. Collins, W.W. Hess (1972). "Aldehydes from Primary Alcohols by Oxidation with Chromium Trioxide: Heptanal". 52: 5. doi:10.15227/orgsyn.052.0005. Cite journal requires |journal= (help)
  14. Horvat, Gordan; Portada, Tomislav; Stilinović, Vladimir; Tomišić, Vladislav (2007). "Tetrapyridinecopper(I) hexafluoridophosphate(V)". Acta Crystallographica Section e Structure Reports Online. 63 (6): m1734. doi:10.1107/S1600536807024051.
  15. Liptay, G.; Wadsten, T.; Borbély-Kuszmann, A. (1986). "Characterization of [Ni(py)4]Cl2 and its thermal decomposition". Journal of Thermal Analysis. 31 (4): 845–852. doi:10.1007/BF01913555.
  16. Nilsson, Karin; Oskarsson, Åke; Lund, P.-A.; Shen, Quang; Weidlein, Johan; Spiridonov, V. P.; Strand, T. G. (1982). "The Crystal Structure of Tetrapyridine Copper(I) Perchlorate and Tetrapyridine Silver(I) Perchlorate at 260 K". Acta Chemica Scandinavica. 36a: 605–610. doi:10.3891/acta.chem.scand.36a-0605.
  17. Corbo, Robert; Georgiou, Dayne C.; Wilson, David J. D.; Dutton, Jason L. (2014). "Reactions of [PhI(pyridine)2]2+ with Model Pd and Pt II/IV Redox Couples". Inorganic Chemistry. 53 (3): 1690–1698. doi:10.1021/ic402836d. PMID 24409820.
  18. Wei, C. H.; Hingerty, B. E.; Busing, W. R. (1989). "Structure of tetrakis(pyridine)platinum(II) chloride trihydrate: Unconstrained anisotropic least-squares refinement of hydrogen and non-hydrogen atoms from combined X-ray–neutron diffraction data". Acta Crystallographica Section C Crystal Structure Communications. 45: 26–30. doi:10.1107/S0108270188009515.
  19. Corbo, Robert; Ryan, Gemma F.; Haghighatbin, Mohammad A.; Hogan, Conor F.; Wilson, David J. D.; Hulett, Mark D.; Barnard, Peter J.; Dutton, Jason L. (2016). "Access to the Parent Tetrakis(pyridine)gold(III) Trication, Facile Formation of Rare Au(III) Terminal Hydroxides, and Preliminary Studies of Biological Properties". Inorganic Chemistry. 55 (6): 2830–2839. doi:10.1021/acs.inorgchem.5b02667. PMID 26930516.
  20. Chirik, Paul J. (2015). "Iron- and Cobalt-Catalyzed Alkene Hydrogenation: Catalysis with Both Redox-Active and Strong Field Ligands". Accounts of Chemical Research. 48 (6): 1687–1695. doi:10.1021/acs.accounts.5b00134. PMID 26042837.
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