User:Indiacox/Dicarbonyldi-μ-chlorodichlorodiplatinum

Trans-Dicarbonyldi-μ-chlorodichlorodiplatinum is the first ever isolated metal-carbonyl complex. It was first synthesized by Paul Schützenberger in 1868.^[1] This discovery of ${\ce {[Pt(CO)Cl2]2}}$ opened the door for the exploration of metal-carbonyl complexes and represents a significant breakthrough in the field of organometallic chemistry.^[1] Though ${\ce {[Pt(CO)Cl2]2}}$ itself is not used in industry, metal carbonyls are an important class of catalysts for a wide range of industrial processes including hydroformylation amongst others.^[2] As such, the discovery of ${\ce {[Pt(CO)Cl2]2}}$ was an important milestone both in the synthesis of organometallic compounds and in the development of many important catalysts widely used today.

Structure and Characterization[edit]

It should be noted that dicarbonyldi-μ-chlorodichlorodiplatinum has both cis and trans isomers. Unless noted otherwise, ${\ce {[Pt(CO)Cl2]2}}$ in this article specifically refers to the trans isomer.

Crystal Structure[edit]

The crystal structure of ${\ce {[Pt(CO)Cl2]2}}$ has been obtained. ${\ce {[Pt(CO)Cl2]2}}$ can be roughly thought of as two square planar ${\ce {Pt(CO)Cl3}}$ centers, but the complex does not perfectly align with that model; the two platinum centers deviate from the square planar geometry of ${\ce {Pt(Cl)3CO}}$ monomers. The μ-chloro ligands and the ${\ce {CO}}$ ligand on each ${\ce {Pt}}$ center are coplanar, but the terminal ${\ce {Cl}}$ on both ${\ce {Pt}}$ centers is 0.228 Å out of plane, giving the complex overall ${\ce {C2}}$ symmetry.^[3] Additionally, the bridging chlorines are not equally shared between the two ${\ce {Pt}}$ centers.^[3]

Spectroscopic Characterization[edit]

IR spectroscopy and NMR have also both been used to characterize ${\ce {[Pt(CO)Cl2]2}}$ . The CO stretching frequency for ${\ce {[Pt(CO)Cl2]2}}$ is 2139 cm^-1 in DCM (the C-O stretching frequency has also been measured in thionyl chloride, cyclohexane and benzene, toluene and n-heptane).^[4] ${\ce {^{195}Pt}}$ NMR reveals two ${\ce {Pt}}$ peaks for ${\ce {[Pt(CO)Cl2]2}}$ (at 1507 and 1511 ppm) in thionyl chloride. This is believed to be due to the formation of two distinct ${\ce {Pt}}$ dimers in solution (where solvation effects cause slight changes in ${\ce {Pt}}$ chemical shift) or stacking of dimers in solution giving rise to distinct ${\ce {Pt}}$ shifts.^[5] ${\ce {^{13}C}}$ NMR reveals a 139.9 shift for the carbonyl carbons with a ${\ce {^{195}Pt ^{13}C}}$ coupling constant of 1958.8Hz.^[6]

Synthesis[edit]

Schützenberger's discovery of ${\ce {[Pt(CO)Cl2]2}}$ [edit]

Compounds synthesized by Schutzenberger from ${\ce {Pt}}$ sponge, ${\ce {Cl2}}$ and ${\ce {CO}}$ . ${\ce {[PtCl2(CO)]2}}$ is favored at high temperatures

Schützenberger first synthesized ${\ce {[Pt(CO)Cl2]2}}$ in 1868.^[1]^[7] The complex was sourced from ${\ce {Pt}}$ black and ${\ce {CO}}$ and ${\ce {Cl2}}$ gases, but there are conflicting reports on whether he flowed a mixture of the gasses over platinum black or first formed ${\ce {PtCl2}}$ and subsequently exposed the compound to ${\ce {CO}}$ .^[3]^[7] However, Schützenberger's isolated product is consistently reported to be a volatile yellow solid. Schützenberger also observed that performing the reaction at different temperatures yields compounds with different melting points.^[7] Based on this observation, Schützenberger identified that the composition of the platinum complex formed under these conditionsis determined by the temperature at which the reaction proceeds. ${\ce {Pt(CO)2Cl2}}$ is formed at a narrow temperature range with this procedure, but the diplatinum complex (and liberation of two ${\ce {CO}}$ equivalents) is favored at higher temperatures.^[7]

More Recent Syntheses[edit]

More recently, ${\ce {[Pt(CO)Cl2]2}}$ has been accessed from other platinum complexes. Dell'Amico et al. reported the formation of ${\ce {[Pt(CO)Cl2]2}}$ from the dimerization of trans- ${\ce {[PtCI2(NCEt)(CO)]}}$ with the production of 2 equivalents of ${\ce {EtCN}}$ as a byproduct.^[8] To obtain ${\ce {[Pt(CO)Cl2]2}}$ , cis- ${\ce {[PtCI2(NCEt)(CO)]}}$ is dissolved in dry mesitylene.^[8] The solution is then heated, allowing the solvent to evaporate. ${\ce {^{195}Pt}}$ NMR analysis of the resulting solid reveals a mixture of of trans- ${\ce {[PtCI2(NCEt)(CO)]}}$ and ${\ce {[Pt(CO)Cl2]2}}$ .^[8] Repeating this dissolution/evaporation procedure yields an orange residue showing complete conversion to ${\ce {[Pt(CO)Cl2]2}}$ .^[8]

Synthesis of ${\ce {[Pt(CO)Cl2]2}}$ from ${\ce {Pt(CO)(NCEt)Cl2}}$ .

Solution phase synthesis of ${\ce {[Pt(CO)Cl2]2}}$ from ${\ce {PtCl4^{2-}}}$ .

Alternatively, ${\ce {[Pt(CO)Cl2]2}}$ has been prepared from

${\ce {Pt(CO)Cl3^-}}$ .^[3] ${\ce {Pt(CO)Cl3^-}}$ can be generated in chlorinated solvents by treating ${\ce {PtCl4^{2-}}}$ with ${\ce {AlCl3}}$ under a ${\ce {CO}}$ atmosphere.^[3] ${\ce {Pt(CO)Cl3^-}}$ can also be accessed by allowing ${\ce {PtCl4^{2-}}}$ to equilibrate under a ${\ce {CO}}$ atmosphere at room temperature, but this equilibration occurs over the course of approximately 40 hours.^[3] ${\ce {[Pt(CO)Cl2]2}}$ can then be generated from ${\ce {Pt(CO)Cl3^-}}$ by treatment with ${\ce {AlCl3}}$ under a nitrogen atmosphere. Interestingly, treating ${\ce {Pt(CO)Cl3^-}}$ with ${\ce {AlCl3}}$ under a ${\ce {CO}}$ atmosphere, trans- ${\ce {Pt(CO)2Cl2}}$ is formed instead.^[3]

Reactivity[edit]

Dissociation of ${\ce {[Pt(CO)Cl2]2}}$ into ${\ce {Pt(CO)2Cl2}}$ .

Olefin addition to ${\ce {[PtCl2(CO)]2}}$ .

${\ce {[Pt(CO)Cl2]2}}$ can dissociate into mono-platinum complexes. By dissolving ${\ce {[Pt(CO)Cl2]2}}$ in thionyl chloride and exposing the solution to atmospheric pressure of ${\ce {CO}}$ at room temperature, ${\ce {Pt(CO)2Cl2}}$ is formed.^[5] Interestingly, trans- ${\ce {Pt(CO)2Cl2}}$ is observed shortly after exposure to ${\ce {CO}}$ , but after allowing the reaction to proceed for 24 hours, the cis isomer is exclusively observed.^[5] Trans- ${\ce {Pt(CO)2Cl2}}$ can also be isolated from ${\ce {[Pt(CO)Cl2]2}}$ by performing the reaction at -80°C. This reaction is observed to be complete after 10 hours. Trans- ${\ce {Pt(CO)2Cl2}}$ is stable at -80°C, but rapidly converts to the cis isomer at room temperature.^[5] Alternatively, olefin substitution can cause the dissociation of the diplatinum complex.^[9] ${\ce {[Pt(CO)Cl2]2}}$ and an olefin (cyclohexene, ethylene or propylene) can be combined in toluene, causing the dissociation of the diplatinum complex to form two equivalents of cis- ${\ce {PtCl2(CO)(olefin)}}$ .^[9]

${\ce {[Pt(CO)Cl2]2}}$ has also been explored as a molecular precursor for loading platinum onto silica (which has been subsequently used to hydrogenate cyclohexene on a laboratory scale).^[10] To do so, dry silica is treated with ${\ce {[Pt(CO)Cl2]2}}$ in toluene at room temperature under a nitrogen atmosphere.^[10] The ${\ce {Pt}}$ containing fragments appear to migrate to the surface of the silica based on the orange color of the material after treatment. Authors attribute this color change to adsorption of a ${\ce {Pt}}$ center onto the ${\ce {SiO2}}$ surface followed by cleavage of the μ-chloro linkages to form surface bound ${\ce {PtCl2(CO)}}$ species.^[10] The treated ${\ce {SiO2}}$ particles were then recovered by filtration and exposed to water vapor at 40°C to liberate ${\ce {CO2}}$ and ${\ce {HCl}}$ , leaving metallic ${\ce {Pt}}$ loaded on silica.^[10]

Overall reaction for ${\ce {Pt}}$ loading onto silica nanoparticles from ${\ce {[PtCl2(CO)]2}}$ .

${\ce {[Pt(CO)Cl2]2}}$ has also been used as a starting material for the formation of more complicated platinum containing complexes. Panuzi et al. report the formation of a diplatinum complex formed by reacting a functionalized xanthene with ${\ce {[Pt(CO)Cl2]2}}$ (shown in the figure below). To synthesize the bidentate xanthene ligand, 4,5-dibromo-2,7-di-tert-butyl-9,9-dimethylxanthene and excess ${\ce {CuCN}}$ are refluxed in dry quinoline for 24 hours. The resulting solid is then washed with diethyl ether and extracted into chloroform. The solid is then purified on a silica column with a 40:1 DCM:methanol eluent (40% yield). To form the platinum complex, the synthesized ligand is combined with excess ${\ce {[Pt(CO)Cl2]2}}$ in toluene. The mixture was allowed to stand overnight at 5°C, where yellow crystals formed. These crystals were then isolated and washed with dry toluene, yielding the pure diplatinum xanthene complex.^[11]

Synthesis of other complexes from ${\ce {[Pt(CO)Cl2]2}}$ .

Catalytic hydrochlorination of cyclohexene.

${\ce {[Pt(CO)Cl2]2}}$ has also been reported as a pre-catalyst for the ${\ce {Pt}}$ catalyzed hydrochlorination of cyclohexene. ^[9] Alper et al. report the reaction of ${\ce {Pt(CO)Cl2(C6H10)}}$ and ${\ce {HCl}}$ to form ${\ce {[Pt(CO)Cl2]2}}$ and liberate ${\ce {C6H11Cl}}$ . ${\ce {[Pt(CO)Cl2]2}}$ can then be reacted with two equivalents of cyclohexene to regenerate ${\ce {Pt(CO)Cl2(C6H10)}}$ .^[9] The overall reaction from these two steps is the catalyzed chlorination of cyclohexene.^[9]

References[edit]

^ ^a ^b ^c Elschenbroich, Christoph (2006). Organometallics (3rd ed.). Weinheim: Wiley-VCH. ISBN 3-527-29390-6. OCLC 64305455.
^ Comprehensive organometallic chemistry III. D. M. P. Mingos, Robert H. Crabtree (1st ed.). Amsterdam: Elsevier. 2007. ISBN 0-08-052350-1. OCLC 228076728.{{cite book}}: CS1 maint: others (link)
^ ^a ^b ^c ^d ^e ^f ^g Bagnoli, Franco; Belli Dell'Amico, Daniela; Calderazzo, Fausto; Englert, Ulli; Marchetti, Fabio; Merigo, Alessandra; Ramello, Stefano (2001). "Halo-carbonyl complexes of platinum(II) and palladium(II)". Journal of Organometallic Chemistry. 622 (1): 180–189. doi:10.1016/S0022-328X(00)00947-5. ISSN 0022-328X.
^ Calderazzo, Fausto; Dell'Amico, Daniela Belli (1981). "Syntheses of carbonyl halides of late transition elements in thionyl chloride as solvent. Carbonyl complexes of palladium(II)". Inorganic Chemistry. 20 (4): 1310–1312. doi:10.1021/ic50218a072. ISSN 0020-1669.
^ ^a ^b ^c ^d Belli Dell'Amico, Daniela; Calderazzo, Fausto; Veracini, Carlo Alberto; Zandona, Nicola (1984). "Comparison between carbonyl derivatives of palladium and those of nickel and platinum". Inorganic Chemistry. 23 (19): 3030–3033. doi:10.1021/ic00187a027. ISSN 0020-1669.
^ Andreini, Bianca Patrizia; Belli Dell'Amico, Daniela; Calderazzo, Fausto; Venturi, Maria Giovanna; Pelizzi, Giancarlo; Serge, Annalaura (1988). "Carbonyl complexes of noble metals with halide ligands". Journal of Organometallic Chemistry. 354 (3): 357–368. doi:10.1016/0022-328X(88)80661-2.
^ ^a ^b ^c ^d Wisniak, Jaime (2015). "Paul Schützenberger". Educación Química (in Spanish). 26 (1): 57–65. doi:10.1016/S0187-893X(15)72100-2.
^ ^a ^b ^c ^d Dell'Amico, Daniela Belli; Labella, Luca; Marchetti, Fabio; Samaritani, Simona (2012). "A convenient route to dinuclear chloro-bridged platinum( ii ) derivatives vianitrile complexes". Dalton Trans. 41 (4): 1389–1396. doi:10.1039/C1DT11709B. ISSN 1477-9226.
^ ^a ^b ^c ^d ^e Alper, Howard; Huang, Yujin; Belli Dell'Amico, Daniela; Calderazzo, Fausto; Pasqualetti, Nicola; Veracini, Carlo Alberto (1991). "Synthesis of carbonyl-olefin complexes of platinum(II), PtX2(CO)(olefin), and the catalytic hydrochlorination of olefins". Organometallics. 10 (6): 1665–1671. doi:10.1021/om00052a010. ISSN 0276-7333.
^ ^a ^b ^c ^d Armelao, Lidia; Belli Dell’Amico, Daniela; Braglia, Roberto; Calderazzo, Fausto; Garbassi, Fabio; Marra, Gianluigi; Merigo, Alessandra (2009). "Loading silica with metals (palladium or platinum) under mild conditions by using well-defined molecular precursors". Dalton Transactions (28): 5559. doi:10.1039/b903655e. ISSN 1477-9226.
^ Panunzi, Achille; Giordano, Federico; Orabona, Ida; Ruffo, Francesco (2005). "Binuclear platinum complexes of 4,5-disubstituted xanthenes". Inorganica Chimica Acta. 358 (4): 1217–1224. doi:10.1016/j.ica.2004.11.034.

[:0-1] Elschenbroich, Christoph (2006). Organometallics (3rd ed.). Weinheim: Wiley-VCH. ISBN 3-527-29390-6. OCLC 64305455.

[2] Comprehensive organometallic chemistry III. D. M. P. Mingos, Robert H. Crabtree (1st ed.). Amsterdam: Elsevier. 2007. ISBN 0-08-052350-1. OCLC 228076728.{{cite book}}: CS1 maint: others (link)

[:1-3] ^ ^a ^b ^c ^d ^e ^f ^g Bagnoli, Franco; Belli Dell'Amico, Daniela; Calderazzo, Fausto; Englert, Ulli; Marchetti, Fabio; Merigo, Alessandra; Ramello, Stefano (2001). "Halo-carbonyl complexes of platinum(II) and palladium(II)". Journal of Organometallic Chemistry. 622 (1): 180–189. doi:10.1016/S0022-328X(00)00947-5. ISSN 0022-328X.

[4] Calderazzo, Fausto; Dell'Amico, Daniela Belli (1981). "Syntheses of carbonyl halides of late transition elements in thionyl chloride as solvent. Carbonyl complexes of palladium(II)". Inorganic Chemistry. 20 (4): 1310–1312. doi:10.1021/ic50218a072. ISSN 0020-1669.

[:2-5] Belli Dell'Amico, Daniela; Calderazzo, Fausto; Veracini, Carlo Alberto; Zandona, Nicola (1984). "Comparison between carbonyl derivatives of palladium and those of nickel and platinum". Inorganic Chemistry. 23 (19): 3030–3033. doi:10.1021/ic00187a027. ISSN 0020-1669.

[6] Andreini, Bianca Patrizia; Belli Dell'Amico, Daniela; Calderazzo, Fausto; Venturi, Maria Giovanna; Pelizzi, Giancarlo; Serge, Annalaura (1988). "Carbonyl complexes of noble metals with halide ligands". Journal of Organometallic Chemistry. 354 (3): 357–368. doi:10.1016/0022-328X(88)80661-2.

[:3-7] Wisniak, Jaime (2015). "Paul Schützenberger". Educación Química (in Spanish). 26 (1): 57–65. doi:10.1016/S0187-893X(15)72100-2.

[:4-8] Dell'Amico, Daniela Belli; Labella, Luca; Marchetti, Fabio; Samaritani, Simona (2012). "A convenient route to dinuclear chloro-bridged platinum( ii ) derivatives vianitrile complexes". Dalton Trans. 41 (4): 1389–1396. doi:10.1039/C1DT11709B. ISSN 1477-9226.

[:6-9] Alper, Howard; Huang, Yujin; Belli Dell'Amico, Daniela; Calderazzo, Fausto; Pasqualetti, Nicola; Veracini, Carlo Alberto (1991). "Synthesis of carbonyl-olefin complexes of platinum(II), PtX2(CO)(olefin), and the catalytic hydrochlorination of olefins". Organometallics. 10 (6): 1665–1671. doi:10.1021/om00052a010. ISSN 0276-7333.

[:5-10] Armelao, Lidia; Belli Dell’Amico, Daniela; Braglia, Roberto; Calderazzo, Fausto; Garbassi, Fabio; Marra, Gianluigi; Merigo, Alessandra (2009). "Loading silica with metals (palladium or platinum) under mild conditions by using well-defined molecular precursors". Dalton Transactions (28): 5559. doi:10.1039/b903655e. ISSN 1477-9226.

[11] Panunzi, Achille; Giordano, Federico; Orabona, Ida; Ruffo, Francesco (2005). "Binuclear platinum complexes of 4,5-disubstituted xanthenes". Inorganica Chimica Acta. 358 (4): 1217–1224. doi:10.1016/j.ica.2004.11.034.

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