Reactivity of Tin(II) Guanidinate with 1,2- and 1,3-Diones: Oxidative Cycloaddition or Ligand Substitution ?

Abstract

A series of tin(IV) guanidinates were prepared by a (4+1) oxidative cycloaddition of four 1,2-diones (3,5-di-tertbutyl-o-benzoquinone, 3,4,5,6-tetrachloro-1,2-benzoquinone, 9,10-phenanthrenedione, 1,2-diphenylethanedione) or by an oxidative addition of a C−Br bond (from 2-bromo-1,3-diphenylpropane-1,3-dione followed by rearrangement) and a Cl−Cl bond (Cl 2 generated from (dichloro-λ 3 -iodanyl)benzene) with {pTol-NC[N(SiMe 3 ) 2 ]N-pTol} 2 Sn (1). The reactivity of five pentane-1,3-diones and dimethyl malonate with compound 1 was assessed on the basis of the effect of 1,3-diones on the reaction mechanism in comparison with 1,2-diones. In contrast with oxidation reactions observed for compounds containing conjugated CO bonds, the reactions of the tin(II) guanidinate with 1,3-diones revealed a high ability for ligand substitution. All the tin compounds prepared were characterized, and ligand substitution reactions were monitored using 1 H, 13 C, and 119 Sn NMR spectroscopy. The molecular structures of one tin(II) and five tin(IV) guanidinato complexes investigated were determined by Xray diffraction. All tin(IV) compounds display six-or seven-coordination. The UV−vis absorption spectra were recorded and simulated by TDDFT methods in order to get insight into the origin of the nontypical colors of the target tin(IV) diolatoguanidinates and their keto-functionalized precursors.

Oxidative Additions of Homoleptic Tin(II) Amidinate

“…Homoleptic amidinatostannylene 1 is thus able to overcome the higher energy barrier in the activation of oxygen molecules (O 2 dissociation energy is 497 kJ mol −1 13 ) under mild conditions compared to homoleptic tin(II) guanidinate {pTol−NC[N(SiMe 3 ) 2 ]N−pTol} 2 Sn. 12 The differences between both stannylenes (amidinate vs guanidinate) are also evident from the molecular orbital distribution in both compounds as well as HOMO−LUMO gaps (see Figure S1, Supporting Information) almost due to the presence of aromatic substituents on the guanidinate. The HOMO orbital in guanidinate corresponds to a π orbital located on the Tol substituents, whereas in amidinate, to an nstype orbital on Sn(II).…”

“…This phenomenon has also been described for the similar reactions of {pTol NC[N(SiMe 3 ) 2 ]NpTol} 2 Sn. 12 Ligand mono-and/or disubstitution products as well as amidine CyNC(nBu)NHCy 14 (LH) always resulted in inseparable oily mixtures (except for 10, see Scheme 1) where all the species have been easily identified by the help of 13 C and 119 Sn NMR spectroscopy (see below). Tin(II) amidinato-dionate 10 (Scheme 1), as the ligand monosubstitution product of reaction of 1 with PhC(C O)CH 2 (CO)Ph, was obtained in the form of orange powder (69%) after removal of LH by hexane extraction.…”

“…This phenomenon was also observed for the series of tin(IV) guanidinato-diolates. 12 The signal of the carbon atom in the OC(O)O structural motive of oxocarbonate 9 in 13 C NMR spectra is solvent independent (resonates at 159.3 ppm/J C,Sn = 30 Hz in C 6 D 6 or 159.0 ppm/J C,Sn = 30 Hz in THF-d 8 solution) and comparable with distanna-oxocarbonate 15 (L CN 2 Sn) 2 (μ-O)(μ-CO 3 ) -161.9 ppm; J C,Sn = 22 Hz.…”

“…The interatomic Sn−Cl distances (2.4134 (6) and 2.3981 (6) The structure of stannylene 10 ( Figure 5) with a fourcoordinated tin atom has a disordered tetragonal pyramidal geometry with the lone electron pair of the tin(II) atom situated perpendicularly to the base formed by two donor nitrogen N1 and N2 and oxygen O1 and O2 atoms (analogous to tin(II) guanidinato-dionate 12 as tin(II) bis(1,3-diphenylpropan-1,3-dionate) (∼2.2 Å, ∼78.2°). 24 UV−vis Absorption and Computational DFT Studies.…”

“…This phenomenon was also observed and discussed for the series of tin(IV) guanidinato-diolates. 12 The absorption spectra of the rest of the appropriate 1,2-diones were published elsewhere. 12 The spectrum of colorless [Cy− NC(nBu)N−Cy] 2 Sn 1 was not recorded (instability in CH 2 Cl 2 ).…”