Tin(II) Ureide Complexes: Synthesis, Structural Chemistry, and Evaluation as SnO Precursors

Abstract

In an attempt to tailor precursors for application in the deposition of phase pure SnO, we have evaluated a series of tin (1–6) ureide complexes. The complexes were successfully synthesized by employing N,N′-trialkyl-functionalized ureide ligands, in which features such as stability, volatility, and decomposition could be modified with variation of the substituents on the ureide ligand in an attempt to find the complex with the ideal electronic, steric, or coordinative properties, which determine the fate of the final products. The tin­(II) ureide complexes 1-6 were synthesized by direct reaction [Sn­{NMe2}2] with aryl and alkyl isocyanates in a 1:2 molar ratio. All the complexes were characterized by NMR spectroscopy as well as elemental analysis and, where applicable, thermogravimetric (TG) analysis. The single-crystal X-ray diffraction studies of 2, 3, 4, and 6 revealed that the complexes crystallize in the monoclinic space group P2­(1)/n (2 and 4) or in the triclinic space group P-1 (3 and 6) as monomers. Reaction with phenyl isocyanate results in the formation of the bimetallic species 5, which crystallizes in the triclinic space group P-1, a consequence of incomplete insertion into the Sn-NMe2 bonds, versus mesityl isocyanate, which produces a monomeric double insertion product, 6, under the same conditions, indicating a difference in reactivity between phenyl isocyanate and mesityl isocyanate with respect to insertion into Sn-NMe2 bonds. The metal centers in these complexes are all four-coordinate, displaying either distorted trigonal bipyramidal or trigonal bipyramidal geometries. The steric influence of the imido-ligand substituent has a clear effect on the coordination mode of the ureide ligands, with complexes 2 and 6, which contain the cyclohexyl and mesityl ligands, displaying κ2-O,N coordination modes, whereas κ2-N,N′ coordination modes are observed for the sterically bulkier tert-butyl and adamantyl derivatives, 3 and 4. The thermogravimetric analysis of the complexes 3 and 4 exhibited excellent physicochemical properties with clean single-step curves and low residual masses in their TG analyses suggesting their potential utility of these systems as MOCVD and ALD precursors.

Oxidative Addition of Alkyl Iodides to [Sn(NMe2)2]2: In Situ Generation of RSn(NMe2)3 Compounds

“…The observed T 50 -values (120–137 °C), the temperature at which 50% of the mass remains, correlate well with precursor identity, i.e., heavier compounds display larger T 50 -values (Table ). By TGA, 1 exhibits comparable performance to reported N-coordinated Sn­(II) pyrrolides and ureides that were similarly screened as MOCVD precursors. , However, 3 – 5 and 10 demonstrate desirable volatility by TGA, with lower T 50 - and residual mass values as compared to 1 . Overall, the tin amides examined are volatile liquids that are promising candidates for vapor deposition of tin-containing films.…”

“…By TGA, 1 exhibits comparable performance to reported N-coordinated Sn(II) pyrrolides and ureides that were similarly screened as MOCVD precursors. 27,111 However, 3−5 and 10 demonstrate desirable volatility by TGA, with lower T 50 -and residual mass values as compared to 1. Overall, the tin amides examined are volatile liquids that are promising candidates for vapor deposition of tin-containing films.…”

“…Tin metal is used in alloys (e.g., bronze), solders, food packaging, and as a plasma source for high energy lasers (EUV photolithography). − Organotin chemistry has similarly found commercial applications such as plastics stabilizers (PVC), fungicides, biocides (e.g., wood preservatives and antifouling coatings on ship hulls), and impact resistant coatings on glass containers. − However, concerns over toxicity and persistence in the biosphere have limited many of these applications. − Organic transformations, most notably the eponymous Stille coupling, utilize organotin reagents (e.g., RSn n Bu 3 ), facilitating Pd-catalyzed cross-coupling of carbon–carbon bonds to generate value-added products. − Organometallic tin compounds are used in the semiconductor industry as chemical vapor deposition (CVD) and atomic layer deposition (ALD) precursors for growing tin-containing films. For example, the oxides of tin, p-type SnO, − and n-type SnO 2 , , are transparent conducting oxides (TCOs); the most widely studied of which are tin-doped indium oxide (ITO) films. − These materials combine optical transparency and electrical conductivity, finding extensive applications in optoelectronics, thin film transistors (TFTs), photovoltaics, and light emitting diodes. − Furthermore, functionalized tin oxide clusters have demonstrated utility as next-generation photoresists (metal-oxide resists) supporting extreme ultraviolet (EUV) photolithography processes. Tin-based inorganic photoresists offer increased photoemission cross-sectional absorbance in the EUV region (13.5 nm) compared to traditional organic spin-on resists, minimizing stochastic defects and improving resolution (e.g., line edge roughness) during lithography. , Recently, Brainard and coworkers demonstrated a 10.5 fold enhancement of EUV light absorbance in alkylated tin-oxide clusters as compared to organic resists …”

Heteroallene Insertions into Tin(II) Alkoxide Bonds

“…As part of continuing interest in tetrylene chemistry [R 2 E] (E = Ge Sn or Pb) and the development of precursors for the deposition of thin films of both SnO , and SnS, − we describe here the synthesis and characterization of tin­(II) iso-carbamate and alkyl carbonate compounds through the insertion reactions of organic isocyanates and CO 2 , respectively, into the Sn–OR bond of tin­(II) alkoxides.…”