Transition metal nitrile complexes

File:A5Ru(NCPh).png

According to the Covalent bond classification method, nitriles are classified as L ligands, i.e., charge-neutral Lewis bases. With respect to HSAB theory, they are classified as soft.

Typical nitrile ligands are acetonitrile, propionitrile, and benzonitrile. The structures of [Ru(NH₃)₅(NCPh)]ⁿ⁺ have been determined for the 2+ and 3+ oxidation states. Upon oxidation the Ru-NH₃ distances contract and the Ru-NCPh distances elongate, consistent with amines serving as pure-sigma donor ligands and nitriles functioning as pi-acceptors.{{cite journal |doi=10.1021/ic9700967|title=Electronic and Molecular Structures of Pentaammineruthenium Pyridine and Benzonitrile Complexes as a Function of Oxidation State|year=1997|last1=Shin|first1=Yeung-gyo K.|last2=Szalda|first2=David J.|last3=Brunschwig|first3=Bruce S.|last4=Creutz|first4=Carol|last5=Sutin|first5=Norman|journal=Inorganic Chemistry|volume=36|issue=14|pages=3190–3197|pmid=11669976}}

Acetonitrile, propionitrile and benzonitrile are also popular solvents. Because nitrile solvents have high dielectric constants, cationic complexes containing a nitrile ligand are often soluble in a solution of that nitrile.

Some complexes can be prepared by dissolving an anhydrous metal salt in the nitrile. In other cases, a suspension of the metal is oxidized with a solution of NOBF₄ in the nitrile:{{cite journal|doi = 10.1002/0471224502.ch2 |journal = Inorg. Synth.| volume = 33 | pages = 75–83 | title = Homoleptic Transition Metal Acetonitrile Cations with Tetrafluoroborate or Trifluoromethanesulfonate Anions |first1=Robert A. |last1=Heintz|first2=Jennifer A.|last2=Smith |first3=Paul S.|last3=Szalay |first4=Amy|last4=Weisgerber |first5=Kim R.|last5=Dunbar | year=2002}}

:Ni + 6 MeCN + 2 NOBF₄ → [Ni(MeCN)₆](BF₄)₂ + 2 NO

Heteroleptic complexes of molybdenum and tungsten can by synthesized from their respective hexacarbonyl complexes.{{cite journal|doi = 10.1002/9780470132593.ch14 |journal = Inorganic Syntheses | volume = 28 | pages = 63–67 | title = Acetonitrile Complexes of Selected Transition Metal Cations|first1=Richard R. |last1=Thomas|first2=Ayusman|last2=Sen | year=2007|isbn = 9780470132593 }}

:M(CO)₆ + 4 MeCN + 2 NOBF₄ → [M(NO)₂(MeCN)₄](BF₄)₂

File:ACNNIZ.png (ZnCl₄²⁻) salt of [Ni(MeCN)₆]²⁺{{cite journal|doi=10.1107/S0567740876006249|journal=Acta Crystallographica Section B|year=1976|author1=I. Sotofte|author2=R. G. Hazell|author3=S. E. Rasmussen|volume=32|pages=1692–1696|title=Hexaacetonitrilenickel(II) Tetrachlorozincate. A Crystal Structure with Serious Overlap in the Patterson Function|issue=6|doi-access=free}}]]

For the synthesis of some acetonitrile complexes, the nitrile serves as a reductant. This method is illustrated by the conversion of molybdenum pentachloride to the molybdenum(IV) complex:{{cite book |doi=10.1002/9781118744994.ch03|chapter=Ether Complexes of Molybdenum(III) and Molybdenum(IV) chlorides |series=Inorganic Syntheses| volume =36 |year=2014 |last1=Maria |first1=Sébastien |last2=Poli |first2=Rinaldo |title=Inorganic Syntheses: Volume 36 |pages=15–18|isbn=9781118744994 |url=https://hal.archives-ouvertes.fr/hal-02042499/file/332-10.1002-9781118744994.ch03-Accepted.pdf }}

: 2 MoCl₅ + 5 CH₃CN → 2 MoCl₄(CH₃CN)₂ + ClCH₂CN + HCl

Transition metal nitrile complexes are usually employed because the nitrile ligand is labile and relatively chemically inert. Cationic nitrile complexes are however susceptible to nucleophilic attack at carbon. Consequently some nitrile complexes catalyze the hydrolysis of nitriles to give the amides.{{cite book |doi=10.1016/B0-08-043748-6/01248-2|chapter=Reactivity of Coordinated Nitriles|title=Comprehensive Coordination Chemistry II|year=2003|last1=Pombeiro|first1=A.J.L.|last2=Kukushkin|first2=V.Yu.|pages=639–660|isbn=9780080437484}}

Fe- and Co-nitrile complexes are intermediates in nitrile hydratase enzymes. N-coordination activates the sp-hybridized carbon center toward attack by nucleophiles, including water.{{cite journal |doi=10.1021/ja00315a029|title=Synthesis and base hydrolysis of pentaammine N,N-dimethylformamide and acetonitrile complexes of rhodium(III) and iridium(III)|year=1984|last1=Curtis|first1=Neville J.|last2=Sargeson|first2=Alan M.|journal=Journal of the American Chemical Society|volume=106|issue=3|pages=625–630}}{{cite journal |doi=10.1021/cr020619e |title=Synthetic Analogues of Cysteinate-Ligated Non-Heme Iron and Non-Corrinoid Cobalt Enzymes |date=2004 |last1=Kovacs |first1=Julie A. |journal=Chemical Reviews |volume=104 |issue=2 |pages=825–848 |pmid=14871143 |pmc=4487544 }} Thus coordination of the nitrile to a cationic metal center is the basis for the catalytic hydration:

:M-NCR + H₂O → M-O=C(NH₂)R

:M-O=C(NH₂)R + NCR → O=C(NH₂)R + M-NCR

Nitrile ligands in electron-rich complexes are susceptible to oxidation, e.g. by iodosylbenzene.{{cite journal |doi=10.1016/j.poly.2004.09.008|title=Coordination and reactivity of acetonitrile in tungsten(IV) complexes: Oxidation, methylation and dimerization of coordinated acetonitrile |year=2004 |last1=Cross |first1=Jeffrey L. |last2=Garrett |first2=Andrew D. |last3=Crane |first3=Todd W. |last4=White |first4=Peter S. |last5=Templeton |first5=Joseph L. |journal=Polyhedron |volume=23 |issue=17 |pages=2831–2840 }} Nitriles undergo coupling with alkenes, also involving electron-rich complexes.{{cite journal |doi=10.1021/om00125a008|title=Titanacycles derived from reductive coupling of nitriles, alkynes, acetaldehyde, and carbon dioxide with bis(pentamethylcyclopentadienyl)(ethylene)titanium(II) |year=1985 |last1=Cohen |first1=Steven A. |last2=Bercaw |first2=John E. |journal=Organometallics |volume=4 |issue=6 |pages=1006–1014 }}

• Hexakis(acetonitrile)vanadium(II) tetrachlorozincate ([V(MeCN)₆](ZnCl₄)), green{{cite journal |doi=10.1016/j.ica.2004.10.037|title=A Study of the 8466 Structures Reported in Inorganica Chimica Acta: 52 Space Group Changes and Their Chemical Consequences|year=2005|last1=Clemente|first1=Dore Augusto|journal=Inorganica Chimica Acta|volume=358|issue=6|pages=1725–1748}}
• Hexakis(acetonitrile)chromium(II) bis(tetraphenylborate) ([Cr(MeCN)₆](B(C₆H₅)₄)₂, green{{cite journal |doi=10.1107/S2053229615015739|title=An Investigation of the Electron Density of a Jahn–Teller-Distorted Cr^II Cation: The Crystal Structure and Charge Density of Hexakis(acetonitrile-κN)chromium(II) Bis(tetraphenylborate) Acetonitrile Disolvate|year=2015|last1=Thangavel|first1= Arumugam|last2=Wieliczko|first2=Marika|last3=Scarborough|first3=Christopher|last4=Dittrich|first4=Birger|last5=Bacsa|first5=John|journal=Acta Crystallographica Section C: Structural Chemistry|volume=71|issue=11|pages=936–943|pmid=26524164}}
• Hexakis(acetonitrile)chromium(III) tetrafluoroborate ([Cr(MeCN)₆](BF₄)₃), white{{cite journal |doi=10.1016/j.jpcs.2003.08.020|title=Synthesis and Characterization of Hexakis(acetonitrile)chromium(III) Tetrafluoroborate, [Cr^III(NCMe)₆][BF₄]3. A Nonaqueous Cr^III Source|year=2004|last1=Hatlevik|first1=Øyvind|last2=Arif|first2=Atta M.|last3=Miller|first3=Joel S.|journal=Journal of Physics and Chemistry of Solids|volume=65|pages=61–63}}
• Hexakis(acetonitrile)iron(II) bis(tetrakis(pentafluorophenyl)borate) ([Fe(MeCN)₆](B(C₆F₅)₄)₂, orange{{cite journal |doi=10.1039/C7DT04593J|title=New Reactivity at the Silicon Bridge in Sila[1]ferrocenophanes|year=2018|last1=Musgrave|first1=Rebecca A.|last2=Hailes|first2=Rebekah L. N.|last3=Schäfer|first3=André|last4=Russell|first4=Andrew D.|last5=Gates|first5=Paul J.|last6=Manners|first6=Ian|journal=Dalton Transactions|volume=47|issue=8|pages=2759–2768|pmid=29417116|hdl=1983/9e6d6454-2797-41d2-a75f-ed90363b5bed|s2cid=3406313 |url=https://research-information.bris.ac.uk/ws/files/144073031/accepted_manuscript.pdf|hdl-access=free}}
• Hexakis(acetonitrile)cobalt(II) bis(tetrakis(pentafluorophenyl)borate) ([Co(MeCN)₆](B(C₆F₅)₄)₂, purple{{cite journal |doi=10.1002/ejic.200800201|title=Synthesis and Characterization of Acetonitrile-Ligated Transition-Metal Complexes with Tetrakis(pentafluorophenyl)borate as Counteranions|year=2008|last1=Hijazi|first1=Ahmed K.|last2=Al Hmaideen|first2=Akef|last3=Syukri|first3=Syukri|last4=Radhakrishnan|first4=Narayanan|last5=Herdtweck|first5=Eberhardt|last6=Voit|first6=Brigitte|last7=Kühn|first7=Fritz E.|journal=European Journal of Inorganic Chemistry|volume=2008|issue=18|pages=2892–2898|doi-access=free}}
• Hexakis(acetonitrile)nickel(II) tetrafluoroborate ([Ni(MeCN)₆](BF₄)₂), blue
• Hexakis(acetonitrile)copper(II) bis(tetrakis(pentafluorophenyl)borate) ([Cu(MeCN)₆](B(C₆F₅)₄)₂, pale blue-green solid{{cite journal |doi=10.1002/marc.200600139|title=Isobutene Polymerization Using [CuII(NCMe)6]2+ with Non-Coordinating Anions as Catalysts|year=2007|last1=Hijazi|first1=Ahmed K.|last2=Yeong|first2=Hui Y.|last3=Zhang|first3=Yanmei|last4=Herdtweck|first4=Eberhardt|last5=Nuyken|first5=Oskar|last6=Kühn|first6=Fritz E.|journal=Macromolecular Rapid Communications|volume=28|issue=5|pages=670–675}}
• Hexakis(acetonitrile)ruthenium(II) tetrafluoroborate ([Ru(MeCN)₆](BF₄)₂), white, d_Ru-N = 202 pm.{{cite journal |doi=10.1016/j.ica.2013.02.027|title=Synthesis and Electrochemical characterization of [Ru(NCCH₃)₆]²⁺, Tris(acetonitrile) Tris(pyrazolyl)borate, and Tris(acetonitrile) Tris(pyrazolyl)methane Ruthenium(II) Complexes|year=2013|last1=Underwood|first1=Christopher C.|last2=Stadelman|first2=Bradley S.|last3=Sleeper|first3=Mark L.|last4=Brumaghim|first4=Julia L.|journal=Inorganica Chimica Acta|volume=405|pages=470–476}}
• Hexakis(acetonitrile)rhodium(III) tetrafluoroborate ([Rh(MeCN)₆](BF₄)₃), a yellow solid.{{cite journal |doi=10.1021/ja991130e|title=A Remarkable Family of Rhodium Acetonitrile Compounds Spanning Three Oxidation States and with Nuclearities Ranging from Mononuclear and Dinuclear to One-Dimensional Chains|year=1999|last1=Prater|first1=M. E.|last2=Pence|first2=L. E.|last3=Clérac|first3=R.|last4=Finniss|first4=G. M.|last5=Campana|first5=C.|last6=Auban-Senzier|first6=P.|last7=Jérome|first7=D.|last8=Canadell|first8=E.|last9=Dunbar|first9=K. R.|journal=Journal of the American Chemical Society|volume=121|issue=35|pages=8005–8016}}
• Hexakis(acetonitrile)rhenium(II) tetrafluoroborate ([Re(MeCN)₆](BF₄)₂), a yellow solid.{{cite journal |doi=10.1021/acs.inorgchem.2c02056|title=One Electron Changes Everything: Synthesis, Characterization, and Reactivity Studies of [Re(NCCH3)6]3+ |year=2022 |last1=Bolliger |first1=Robin |last2=Blacque |first2=Olivier |last3=Braband |first3=Henrik |last4=Alberto |first4=Roger |journal=Inorganic Chemistry |volume=61 |issue=46 |pages=18325–18334 |pmid=36169602 |pmc=9682483 |s2cid=252565929 }}
• Hexakis(acetonitrile)rhenium(III) tetrafluoroborate ([Re(MeCN)₆](BF₄)₃), a brown solid.

• [Cr(MeCN)₄](BF₄)₂, blue{{cite journal |doi=10.1039/A708988K|title=Synthesis, characterization, and reactions of tetrakis(nitrile)chromium(II) tetrafluoroborate complexes †|year=1998|last1=Henriques|first1=Rui T.|last2=Herdtweck|first2=Eberhardt|last3=Kühn|first3=Fritz E.|last4=Lopes|first4=André D.|last5=Mink|first5=Janos|last6=Romão|first6=Carlos C.|journal=Journal of the Chemical Society, Dalton Transactions|issue=8|pages=1293–1298}}
• [Cu(MeCN)₄]PF₆, colorless
• [Pd(MeCN)₄](BF₄)₂, yellow{{cite book |doi=10.1002/9780470132593.ch14|chapter=Acetonitrile Complexes of Selected Transition Metal Cations|series=Inorganic Syntheses|year=1990|last1=Thomas|first1=Richard R.|last2=Sen|first2=Ayusman|title=Inorganic Syntheses|pages=63–67|isbn=9780470132593}}

• [Mo₂(MeCN)_8/10](BF₄)₄ blue d(Mo-Mo) = 218, d(Mo-N)_axial = 260, d(Mo-N)_equat = 214 pm{{cite journal |doi=10.1021/ic00004a055|title=Synthesis and characterization of octaacetonitriledimolybdenum(II) tetrafluoroborate|year=1991|last1=Cotton|first1=F. Albert.|last2=Wiesinger|first2=Kenneth J.|journal=Inorganic Chemistry|volume=30|issue=4|pages=871–873}}
• [Tc₂(MeCN)₁₀](BF₄)₄{{cite journal |doi=10.1021/ic00111a040|title=Preparation and Characterization of the Fully Solvated Ditechnetium Cation [Tc₂(CH₃CN)₁₀]⁴⁺|year=1995|last1=Bryan|first1=Jeffrey C.|last2=Cotton|first2=F. Albert|last3=Daniels|first3=Lee M.|last4=Haefner|first4=Steven C.|last5=Sattelberger|first5=Alfred P.|journal=Inorganic Chemistry|volume=34|issue=7|pages=1875–1883}}
• [Re₂(MeCN)₁₀][B(C₆H₃(CF₃)₂)₄]₂,{{cite journal |doi=10.1039/b601463a|title=Syntheses and Reactivity Studies of Solvated Dirhenium Acetonitrile Complexes|year=2006|last1=Bera|first1=Jitendra K.|last2=Schelter|first2=Eric J.|last3=Patra|first3=Sanjib K.|last4=Bacsa|first4=John|last5=Dunbar|first5=Kim R.|journal=Dalton Transactions|issue=33|pages=4011–9|pmid=17028710}} blue; d(Re-Re) = 226, d(Re-N)_axial = 240, d(Re-N)_equat = 205 pm
• [Rh₂(MeCN)₁₀](BF₄)₄, orange; d(Rh-Rh) = 261, d(Re-N)_axial = 219, d(Re-N)_equat = 198 pm

• [Ag(MeCN)₂]B(C₆H₃(CF₃)₂)₄{{cite journal |doi=10.1039/b414060e|title=Organonitrile ligated silver complexes with perfluorinated weakly coordinating anions and their catalytic application for coupling reactions |year=2005 |last1=Zhang |first1=Yanmei |last2=Santos |first2=Ana M. |last3=Herdtweck |first3=Eberhardt |last4=Mink |first4=Janos |last5=Kühn |first5=Fritz E. |journal=New J. Chem. |volume=29 |issue=2 |pages=366–370 |url=http://real.mtak.hu/6989/1/1197218.pdf }}
• [Au(MeCN)₂]SbF₆{{cite journal |doi=10.1021/ja00049a030|title=Bis(carbonyl)gold(I) undecafluorodiantimonate(V), [Au(CO)2][Sb2F11]: Synthesis, vibrational, and carbon-13 NMR study and the molecular structure of bis(acetonitrile)gold(I) hexafluoroantimonate(V), [Au(NCCH3)2][SbF6] |year=1992 |last1=Willner |first1=H. |last2=Schaebs |first2=J. |last3=Hwang |first3=G. |last4=Mistry |first4=F. |last5=Jones |first5=R. |last6=Trotter |first6=J. |last7=Aubke |first7=F. |journal=Journal of the American Chemical Society |volume=114 |issue=23 |pages=8972–8980 }}

• Bis(benzonitrile)palladium dichloride (PdCl₂(PhCN)₂), an orange solid that serves as a source of "PdCl₂"
• Tricarbonyltris(propionitrile)molybdenum(0) (Mo(CO)₃(C₂H₅CN)₃), a source of "Mo(CO)₃". Related Cr and W complexes are known.{{cite book|chapter=Tricarbonyltris(Nitrile) Complexes of Cr, Mo, and W|year=1990|volume=28|first1=Gregory J.|last1=Kubas|first2=Lori Stepan|last2=van der Sluys|title=Inorganic Syntheses|series=Inorganic Syntheses|pages=29–33|doi=10.1002/9780470132593.ch6|isbn=9780470132593}}

Cases are known where nitriles function as η²-ligands. This bonding mode is more common for complexes of low-valence metals, such as Ni(0). Complexes of η²-nitriles are expected to form as transient intermediates in certain metal-catalyzed reactions of nitriles, such as the Hoesch reaction and the hydrogenation of nitriles.

In some cases, η²-nitrile ligands are intermediates that preceded oxidative addition.{{cite journal|author1=Churchill, D.|author2=Shin, J. H.|author3=Hascall, T.|author4=Hahn, J. M.|author5=Bridgewater, B. M.|author6=Parkin, G.|title=The Ansa Effect in Permethylmolybdenocene Chemistry: A [Me₂Si] Ansa Bridge Promotes Intermolecular C−H and C−C Bond Activation|journal= Organometallics|year=1999| volume=18|issue=13 |pages=2403–2406|doi=10.1021/om990195n}}

File:ACEKAU.png)(η²-PhCN){{cite journal|author1=García, J. J. |author2=Arévalo, A. |author3=Brunkan, N. M. |author4=Jones, W. D. |title=Cleavage of Carbon−Carbon Bonds in Alkyl Cyanides Using Nickel(0)|journal=Organometallics|year=2004|volume=23|issue=16|pages=3997–4002|doi=10.1021/om049700t}}]]

• Cyanometalate – coordination compounds containing cyanide ligands (coordinating via C).

{{Coordination complexes}}

Category:Coordination complexes

Category:Hexafluorophosphates

Category:Tetrafluoroborates