Hexacoordinate germanium mixed bischelates with the GeCO 3 Cl 2 ligand environment

Bischelate complexes of germanium with different chelate rings were prepared by double transmetallation. The earlier reported (O,O)-chelate [from the reaction of trichloro(chloromethyl)germane and N,N-dimethyl-2-(trimethylsilyloxy)-2-phenylacetamide (1)], 2-[dichloro(chloromethyl)germyloxy]-N,N-dimethyl-2-phenylacetamide (2) was reacted with trimethylsilylamides, 2,2-dimethyl-3-trimethylsilylbenzo[2H]-1,3-oxazin-4-one (5, B–SiMe3) and 4-methyl-1-trimethylsilylquinolin-2-one (6, Q–SiMe3) resulting in mixed (O,O),(C,O)bischelate complexes, 2-[dichloro[(2,2-dimethyl-4-oxo-2H-benzo[e][1,3]oxazin-3(4H)yl)methyl]germyloxy]-N,N-dimethyl-2-phenylacetamide (7) and 2-[dichloro[(4-methyl-2oxoquinolin-1(2H)-yl)methyl]germyloxy]-N,N-dimethyl-2-phenylacetamide (8). Crystallographic analyses established pentacoordination of germanium in 2 and hexacoordination in 7 and 8; the latter two compounds are the first reported mixed (O,O), (C,O)-bischelate complexes with two O→Ge coordinate bonds.


Scheme 1
In the same communication 6 a preliminary X-ray study revealed complex 2 as the first structurally characterized example of neutral pentacoordinate germanium complexes containing a 2-hydroxycarboxamide moiety with (O,O)-monoanionic bidentate chelate ligands.
In the present paper we report the full X-ray data of monochelate complex 2 and the products of its further transformations into neutral bischelate complexes of hexacoordinate germanium containing mixed (O,O)-and (C,O)-chelate ligands.
The pentacoordinate complex, 2-[dichloro(chloromethyl)germyloxy]-N,N-dimethyl-2phenylacetamide (2) is of particular interest as a starting material for the synthesis of mixed bischelates of hypercoordinated germanium.These chelates can be prepared by reactions similar to those used by us earlier for the synthesis of hypercoordinated germanium complexes from chloro(chloromethyl)dimethylgermane 8a-f or dichlorobis(chloromethyl)germane 8g and Ntrimethylsilylamides and related compounds (for more details see 8d,f ).

N
In the mixed-ligand bischelate complexes 7 and 8 (Figure 2) the two different chelate rings cause noticeable distortions of the Ge(1) coordination polyhedra.The configuration of 7 and 8 with respect to Cl, O(1) and O(1') can be described as trans, with angles O(1)Ge(1)Cl(1) and O(1')Ge(1)Cl(2) smaller than 180º (Table 1).The most pronounced distortion of the coordination polyhedron of Ge( 1) is observed for 8 with the two coordination bonds Ge(1)-O(1) and Ge(1)-O(1') differing by 0.09 Å; the Ge-Cl distances differs by 0.04 Å.The conformation of the fivemembered chelate ring formed by the mandelic amide moiety is a planarized twist with C(2) deviating from the basal plane by 0.16 Å.In 7, the chelate ring formed by the benzoxazinone moiety adopts an envelope conformation with Ge(1) deviating from the basal plane by 0.24 Å.The coordination polyhedron of Ge(1) in 7 is less distorted than in 8 (Table 2).The geometries of two independent molecules A and B in the crystal structure of 7 are nearly identical but with opposite configuration (R and S) of the stereocenters C(2A) and C(2B), respectively.The conformations of the chelate ring formed by mandelic amide moieties are envelopes with deviations of Ge(1A) and Ge(1B) of 0.33 and 0.31 Å, respectively.Similar conformations are adopted by the chelate rings formed by quinolinone moieties; Ge(1A) and Ge(1B) deviate from the basal planes by 0.41 and 0.41 Å, respectively.
It should be noted that the mixed complexes 7 and 8 are the first examples of germanium bischelates with different chelate rings. 12perimental Section General Procedures.The IR spectra of the compounds were recorded as ~5% solutions or as KBr pellets on a Specord IR-75 instrument. 1 H and 13 C NMR spectra were measured on a Varian XL-400 spectrometer (400.1 and 100.6 MHz, respectively).The diffraction measurements were carried out with SMART 1000 CCD and Smart APEX II diffractometers.Selected structural parameters of 2, 7 and 8 are listed in Table 1.Details of crystallographic data and experimental conditions are given in Table 2.All structures were solved by direct method and refined by fullmatrix least-squares technique against F 2 in the anisotropic-isotropic approximation.Hydrogen atoms were located from difference electron density syntheses and refined in rigid body model.All calculations were carried out with the SHELXTL PLUS 5.10 program package. 13rystallographic data for 2, 7, and 8 have been deposited at the Cambridge Crystallographic Data Centre.The CCDC numbers are listed in Table 1.Copies of the data can be obtained free of charge upon application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44(1223)336033; e-mail: deposit@ccdc.cam.ac.uk.2-[Dichloro(chloromethyl)germyloxy]-N,N-dimethyl-2-phenylacetamide (2) 6 and 2,2-dimethyl-3-(trimethylsilyl)-2H-benzo[e] [1,3]oxazin-4(3H)-one (5) 14 were synthesized as reported.(6).Chlorotrimethylsilane (54 g, 0.5 mol) was added dropwise to a solution of 4-methylquinolin-2-one (47.6 g, 0.3 mol) and Et 3 N (50 g, 0.5 mol) in benzene (150 mL).The mixture was refluxed for 2 h.Next day, the precipitate formed was filtered off, the volatiles were removed in vacuo, and the residue was distilled to afford a colorless oil 6 (63 g, 91%); bp 152-153 °C (10 mm Hg).IR (CHCl 3 ): ˜ ν 1670, 1615, 1510 (C=O) cm -1 .

Scheme 3 .
Scheme 3. Preparation of bischelate 7 via reaction a (Method a), and reactions b, c (Method b).

Figure 1 .
Figure 1.ORTEP view of 2. Atoms are presented as thermal ellipsoids at 50% probability.Hydrogen atoms are omitted for clarity.

Figure 2 .
Figure 2. (a) Molecule A in the crystal structure of 7. (b) ORTEP view of 8. Atoms are presented as thermal ellipsoids at 50% probability.Hydrogen atoms are omitted for clarity.

Table 1 .
The structures of complexes 7 and 8 were confirmed by element analyses, IR, 1 H and 13 C NMR spectra.At 45 °C the signals of the NCH 2 protons in 7 and 8 appear as broad AB-quartets.Molecular and crystal structures of complexes 2, 7 and 8 were determined by single crystal X-ray diffraction studies.Selected bond lengths and angles are summarized in Table1; crystallographic parameters and experimental details are given in Table2.Selected structural parameters for structures 2, 7, and 8