Trimethylplatinum iodide

Trimethylplatinum iodide is the organoplatinum complex with the formula [(CH3)3PtI]4. It is a white, air-stable solid that was one of the first σ-alkyl metal complexes reported.[1] It arises from the reaction of potassium hexachloroplatinate with methylmagnesium iodide.[2] The complex exists as a tetramer: a cubane-type cluster with four octahedral Pt(IV) centers linked by four iodides as triply bridging ligands.[3] Due to its stability, it is often utilized as a precursor en route to the synthesis of other organoplatinum compound, such as hydrosilylation catalysts.[4] It is also used as a precursor for forming platinum layers for electronics.[5]

Trimethylplatinum iodide
Names
Other names
Iodotrimethylplatinum(IV)
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.206.221
EC Number
  • 681-046-4
  • InChI=1S/3CH3.HI.Pt/h3*1H3;1H;/q3*-1;;+1/p-1
    Key: ZCSQPOLLUOLHHF-UHFFFAOYSA-M
  • [CH3-].[CH3-].[CH3-].I[Pt]
Properties
C12H36I4Pt4
Molar mass 1468.374 g·mol−1
Appearance white solid
Melting point 190-195 °C
Hazards
GHS labelling:
GHS02: FlammableGHS07: Exclamation mark
Warning
H228, H302, H312, H315, H319, H332, H413
P210, P240, P241, P261, P264, P270, P271, P273, P280, P301+P312, P302+P352, P304+P312, P304+P340, P305+P351+P338, P312, P321, P322, P330, P332+P313, P337+P313, P362, P363, P370+P378, P501
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Synthesis

The first reported procedure was in 1909 by Pope and Peachey, where they treated chloroplatinic acid with excess methylmagnesium iodide.[1] The trimethylated Pt(IV) complex could be isolated as a yellow crystalline solid, which contained iodine impurities.[6] Improvements on the synthesis in later years utilized the more facile hexachloroplatinate reagent, potassium hexachloroplatinate, and the addition of iodomethane to reduce the amount of methylmagnesium that needed to use, which generated more byproducts.[7]

Synthesis of trimethylplatinum iodide using hexachloroplatininate and excess methylmagnesium iodide.


Trimethylplatinum iodide could also be formed from ion exchange using potassium iodide, starting from other trimethylplatinum(IV) complexes such as (CH3)3Pt(NO3) or (CH3)3Pt(SO4).[6]

Structure

Crystallography

The compound exists as a tetramer, crystallizing in a monoclinic unit cell.[3] Each Pt atom is coordinated in pseudo-octahedral geometry, while the tetramer unit is nearly cubic in the Pt-I core. The average Pt-I bond distance is 2.83 Å, while the average Pt-C bond distance is 2.04 Å. The fluoride, bromide, chloride, and pseudohalide (OH, N3, SCN, SMe) analogues [(CH3)3PtX)]4 also exist as tetramers, all forming cubane clusters.[8]

Pt-I bond distance and I-Pt-I bond angles of the cubic tetramer, [(CH3)3PtI]4.

Electronic

The tetramer absorbs in weakly at 436 nm and strongly in the UV (209 nm) region and exhibits a very weak emission of 735 nm at room temperature in the solid state or in glasses of toluene.[9] On the basis of octahedral symmetry, the lower energy absorption is suggested to be a spin-forbidden d-d transition, while the higher energy absorption is proposed to be a ligand-to-metal charge transfer band due to high oxidation state on the Pt. The emission is suggested to be phosphorescence, with metal-metal interactions leading to a large Stokes shift.

Infrared and Raman spectroscopy have also been used to indicate the tetramer structure with cubic breathing modes at very low energies of < 250 cm−1.[10]

Reactivity

The tetramer decomposes, sometime explosively, when heated below at 175 - 200°C, resulting in platinum metal, ethane, and iodomethane.[1] When exposed to UV light in solution, the tetramer can undergo photolysis of two methyl radicals by reductive elimination, forming the brief Pt(II)(CH3)I species.[9] This reactivity is attributed to the ligand-to-metal charge transfer excitation.

Photolytic cleavage of (CH3)3PtI, results in production of transient methyl radicals.

The cubane structure can undergo decomposition by ligand substitution and breaking of the bridging iodine, to form a variety of octahedral organoplatinum complexes. Derived compounds include those with polypyridine,[11] pincer,[12] acetylacetonate,[13] and trispyrazolylborate ligands.[14]

Various octahedral organoplatinum complexes that can be synthesized from trimethylplatinum iodide.

Other applications

Trimethylplatinum iodide has been utilized as a precursor to plate Pt films through chemical vapor deposition or atomic layer deposition.[5] To do so, the complex is thermally decomposed, and the iodide is exchanged with methylcyclopentadienyl. The resulting complex (MeCp)Pt(CH3)3 sublimes near room temperature and, when reacted with hydrogen gas, can plate platinum metal. The plating can also be done in oxidative conditions.[15]

Pt is deposited under reducing conditions after conversion of (CH3)3PtI into methylcyclopentadienyl trimethylplatinum, which can easily sublime.

Like other platinum complexes, the trimethylplatinum iodide complex can lead to hydrosilylation of alkenes.[4] While the tetramer itself cannot catalyze hydrosilylation, when it is heated in dodecane in the presence of olefins and hydrosilanes, the subsequent decomposition of the tetramer can generate platinum species that can perform catalytic homogeneous hydrosilyation. The decomposition can be done photolytically in the crosslinking of silicon rubber.[16]

A proposed mechanism for generation of organoplatinum hydrosilyation catalysts by decomposition of [(CH3)3PtI]4.

See also

References
  1. Pope, William Jackson; Peachey, Stanley John (1909). "LXXIII.—The alkyl compounds of platinum". J. Chem. Soc., Trans. 95: 571–576. doi:10.1039/CT9099500571. ISSN 0368-1645.
  2. Clegg, D. E.; Hall, J. R.; Brubaker, C. H.; Gilbert, G. L.; Dyke, M. (2007-01-05), Muetterties, Earl L. (ed.), "Iodo(trimethyl)platinum(IV)", Inorganic Syntheses, Hoboken, NJ, USA: John Wiley & Sons, Inc., pp. 71–74, doi:10.1002/9780470132418.ch13, ISBN 978-0-470-13241-8, retrieved 2023-03-11
  3. Donnay, G.; Coleman, L. B.; Krieghoff, N. G.; Cowan, D. O. (1968-01-23). "Trimethylplatinum(IV) iodide and its misrepresentation as hexamethyldiplatinum". Acta Crystallographica Section B Structural Crystallography and Crystal Chemistry. 24 (1): 157–159. doi:10.1107/S056774086800186X.
  4. Pratt, Sandra L.; Faltynek, Roberta A. (1984). "Studies on the thermal activation of iodotrimethylplatinum(IV) tetramer: hydrosilation catalyst generation from an inert precursor". Journal of Molecular Catalysis. 24 (1): 47–58. doi:10.1016/0304-5102(84)85038-5.
  5. Xue, Ziling; Strouse, M. Jane; Shuh, David K.; Knobler, Carolyn B.; Kaesz, Herbert D.; Hicks, Robert F.; Williams, R. Stanley (1989). "Characterization of (methylcyclopentadienyl)trimethylplatinum and low-temperature organometallic chemical vapor deposition of platinum metal". Journal of the American Chemical Society. 111 (24): 8779–8784. doi:10.1021/ja00206a002. ISSN 0002-7863.
  6. Hoff, G. R.; Brubaker, C. H. (1968). "Some properties of several trimethylplatinum(IV) compounds". Inorganic Chemistry. 7 (8): 1655–1656. doi:10.1021/ic50066a041. ISSN 0020-1669.
  7. WO2021186087A1, Doppiu, Angelino; Karch, Ralf & Woerner, Eileen, "Trimethylplatinum(iv) iodide", issued 2021-09-23
  8. Donath, H; Avtomonov, E. V; Sarraje, I; von Dahlen, K. -H; El-Essawi, M; Lorberth, J; Seo, B. -S (1998-05-29). "Organoplatinum compounds VII1For part VI see Ref. ([4]b).1: Trimethylplatinum fluoride [(CH3)3PtF]4, the missing link in organoplatinum cluster chemistry: its synthesis, crystal structure and a comparison to the crystal structure of [(CH3)3PtOH]4". Journal of Organometallic Chemistry. 559 (1): 191–196. doi:10.1016/S0022-328X(98)00481-1. ISSN 0022-328X.
  9. Kunkely, H.; Vogler, A. (1991). "Electronic spectra and photochemistry of methyl platinum(IV) complexes". Coordination Chemistry Reviews. 111: 15–25. doi:10.1016/0010-8545(91)84006-Q.
  10. Clegg, D. E.; Hall, J. R. (1970-04-01). "Vibrational spectra of chloro-, bromo- and iodotrimethylplatinum(IV)". Journal of Organometallic Chemistry. 22 (2): 491–496. doi:10.1016/S0022-328X(00)86069-6. ISSN 0022-328X.
  11. Ghosh, Biswa Nath; Topić, Filip; Sahoo, Prasit Kumar; Mal, Prasenjit; Linnera, Jarno; Kalenius, Elina; Tuononen, Heikki M.; Rissanen, Kari (2014-12-02). "Synthesis, structure and photophysical properties of a highly luminescent terpyridine-diphenylacetylene hybrid fluorophore and its metal complexes". Dalton Transactions. 44 (1): 254–267. doi:10.1039/C4DT02728K. ISSN 1477-9234. PMID 25373423.
  12. Mazzeo, Mina; Strianese, Maria; Kühl, Olaf; Peters, Jonas C. (2011-08-23). "Phosphido pincer complexes of platinum: synthesis, structure and reactivity". Dalton Transactions. 40 (35): 9026–9033. doi:10.1039/C1DT10825E. ISSN 1477-9234. PMID 21826355.
  13. Zharkova, G. I.; Baidina, I. A.; Naumov, D. Yu.; Igumenov, I. K. (2011-06-01). "Crystal structure of volatile pyridine adducts of trimethylplatinum(IV) β-diketonates". Journal of Structural Chemistry. 52 (3): 550–555. doi:10.1134/S0022476611030152. ISSN 1573-8779. S2CID 93708060.
  14. Kuchta, Matthew C.; Gemel, Christian; Metzler-Nolte, Nils (2007-02-15). "An amino acid bioconjugate of an organoplatinum tris(pyrazolyl)borate complex: Synthesis and structure of [p-(tBuO–Phe–CO)C6H4Tp]PtMe3". Journal of Organometallic Chemistry. Third International Symposium on Bioorganometallic Chemistry. 692 (6): 1310–1314. doi:10.1016/j.jorganchem.2006.10.028. ISSN 0022-328X.
  15. Hiratani, Masahiko; Nabatame, Toshihide; Matsui, Yuichi; Imagawa, Kazushige; Kimura, Shinichiro (2001). "Platinum Film Growth by Chemical Vapor Deposition Based on Autocatalytic Oxidative Decomposition". Journal of the Electrochemical Society. 148 (8): C524. Bibcode:2001JElS..148C.524H. doi:10.1149/1.1381389.
  16. , Ziche, Wolfgang & Köllnberger, Andreas, "Platinum Complexes and Their Use in Compounds That Can Be Cross-Linked by a Hydrosilylation Reaction", issued 2016-03-03
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