Synthesis, heteronuclear NMR and X-ray crystallographic studies of two dinuclear diorganotin(IV) dithiocarbamate macrocycles

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Introduction
During the last few years the metal ion directed self assembly of ligands to well-defined structures has been exploited mainly in two directions: first, the generation of discrete cyclooligomeric molecular structures having cavities and, second, the creation of microporous coordination polymers. 1For this purpose mainly transition metals and easily available ligands such as carboxylic acids and amines have been applied.The number of reports on systems containing representative elements or organometallic building blocks such as organotin moieties is relatively small so far. 2,3The same is true for the application of dithiocarbamate (dtc) ligands in supramolecular chemistry.Moreover, metallomacrocycles based on dtc ligands are almost unexplored. 4ecently, synthetic strategies have been developed for the preparation of macrocyclic and microporous materials based on diorganotin dicarboxylates. 5In this contribution we present an extension of this strategy to the synthesis of diorganotin(IV) dithiocarbamate macrocycles, the results of which are presented herein.

Synthetic Methods
The secondary diamine, N,N´-dibenzylhexamethylene-1,6-diamine, used as starting material for the preparation of the diorganotin complexes, was obtained in 90% yield by condensation of benzaldehyde with 1,6-hexamethylenediamine in ethanol followed by reduction of the Schiff base with NaBH 4 in methanol. 6One-pot syntheses from this amine, carbon disulfide, triethylamine and R 2 SnCl 2 (R = Me, nBu) gave colorless precipitates that were recrystallized from chloroform and a mixture of dichloromethane/methanol to give the dinuclear diorganotin(IV) dithiocarbamate macrocycles, [Me 2 Sn(dtc)] 2 (1) and [nBu 2 Sn(dtc] 2 (2), in yields of 54 and 36 %, respectively (Scheme 1).These products are soluble in non polar solvents such as dichloromethane and chloroform, but insoluble in polar solvents such as acetone, ethanol, methanol, dimethyl sulfoxide, acetonitrile and water.
The composition and molecular structures of compounds 1 and 2 were established by elemental analysis, mass spectrometry, IR and NMR ( 1 H, 13 C, 119 Sn) spectroscopy, as well as single crystal X-ray crystallography.

Spectroscopic characterization
The IR spectra of 1 and 2 gave evidence for the formation of the dithiocarbamate functions and their coordination to the diorganotin fragments.The bands resulting from the stretching vibrations of the C-N bonds at 1476 and 1475 cm -1 have wavenumbers that are intermediate when compared to those reported for C-N single bonds (1250-1360 cm -1 ) and C=N double bonds (1640-1690 cm -1 ), suggesting partial double bond character and, therefore, partial delocalization of π−electron density within the dithiocarbamate functions. 7For the CS 2 -groups two bands were observed, ν(CS 2 ) as and ν(CS 2 ) s (1239, 981 cm -1 for 1 and 1238, 980 cm -1 for 2), which are characteristic for an anisobidentate chelation mode of the ligands to the metal atoms. 8he 1 H and 13 C NMR spectra of compounds 1 and 2 were assigned completely by 2D correlation experiments (COSY and HSQC).A comparison of the 1 H NMR spectra between the N,N´-dibenzylhexamethylene-1,6-diamine and the resulting products showed significant shift displacements to lower fields for the NCH 2benzyl and NCH 2chain methylene hydrogen atoms (1: ∆δ = 1.39 and 1.02 ppm, 2: ∆δ = 1.42 and 1.07 ppm), thus indicating the formation of the dithiocarbamate complexes.For the corresponding carbon atoms shift displacements in the same direction were observed (1: ∆δ = 3.2 and 4.4 ppm, 2: ∆δ = 3.2 and 4.6 ppm).The NCS 2 carbon atoms gave signals at δ = 201.0 and 201.8 ppm, respectively.Interestingly, in the 1 H NMR spectra all methylene hydrogen atoms gave rise to broad signals, indicating that the complexes are involved in at least one dynamic process.Considering the macrocyclic nature of the products (vide infra), it can be supposed that there exist conformational equilibria in solution.
The 119 Sn RMN spectroscopic data allowed to establish the coordination number of the tin atoms.According to the information reported in the literature, 9 the 119 Sn NMR chemical shift values for compounds 1 (δ = -332 ppm) and 2 (δ = -333 ppm) indicate that the tin atoms are hexa-coordinated in solution.For compound 1 it was possible to measure the 2 J Sn-H coupling constant in the 1 H NMR spectrum (82 Hz).
The assembly of the starting materials described in Scheme 1 can give either cyclooligomeric or polymeric products.The mass spectra (FAB + ) of compounds 1 and 2 support the assumption that dimeric structures had been obtained, since in both cases peaks were only observed in the range corresponding to substances having a dimeric composition.However, the peak corresponding to the molecular ion could be detected only in the case of compound 1, m/z 1190, while for 2 only fragments derived from a dimeric structure could be observed.In this case, one of the most prominent peaks, m/z 1066, corresponds to a dinuclear species, which has suffered loss of one of the N,N´-dibenzylhexamethylene-1,6-diamine fragments (see Experimental Section).

Table 1 .
Crystallographic data for compounds 1 and 2

Table 2 .
Selected bond lengths, bond angles and torsion angles for compounds 1 and 2 ARKAT USA, Inc.