Isocyanate Insertion into a La–P Phosphide Bond: A Versatile Route to Phosphaureate-Bridged Heterobimetallic Lanthanide–Coinage-Metal Complexes

A new route to heterobimetallic lanthanide–coinage-metal complexes is disclosed. The selective insertion of organic substrates such as phenyl iso(thio)cyanate into the La–P bond of the primary phosphido complex (PN)2La(PHMes) (1) (with PN– = (N-(2-(diisopropylphosphanyl)-4-methylphenyl)-2,4,6-trimethylanilide) yields the phospha(thio)ureate complexes (PN)2La(OC(NPh)(PHMes)) (2) and (PN)2La(SC(NPh)(PHMes)) (3) with retention of the PH protons. Subsequent deprotonation of the phosphaureate complex 2 with potassium hexamethyldisilazide (KHMDS, K[N(SiMe3)2]) leads to the polymeric complex [K{(PN)2La(OC(NPh)(PMes))}]n (4). Complex 4 was found to be an excellent precursor for salt metathesis reactions with copper(I) and gold(I) chlorides supported by an N-heterocyclic carbene (NHC, 5 and 6) or a cyclic alkyl amino carbene (CAAC, 7 and 8). This resulted in the unprecedented formation of heterobimetallic lanthanum–coinage-metal complexes, containing the first example of a μ,κ2(O,N):κ1(P)-phosphaureate bridging ligand. For an alternative route to complex 8 a direct protonolysis protocol between a new basic gold(I) precursor, namely (MeCAAC)Au(HMDS), and 2 was also investigated. The complexes have been characterized by multinuclear NMR spectroscopy, IR spectroscopy, and X-ray crystallography (except for 8).

A procedure similar to the one reported by Romanov et al. for ( Et CAAC)AuCl was adapted. 6 To a -78 °C cold suspension of (tht)AuCl (122 mg, 381 µmol, 1 eq.) in THF (10 mL) was added dropwise solution of Me CAAC (109 mg, 381 µmol, 1 eq.) in THF (5 mL) under stirring. The resulting reaction mixture was stirred for 16 h, while warming up to room temperature. This yielded a grey-brown suspension. All volatile components were removed in vacuo and the remaining solid washed with n-hexane (2 x 3 mL). The grey solid was then extracted into dichloromethane (4 mL) and filtered through a glass fibre filter, leaving a black solid on the filter and a brown-red solution. The solvent was removed from the filtrate, leaving a rose-colored solid which 1 H and 13 C{ 1 H} NMR spectroscopy showed to be a mixture of ( Me CAAC)AuCl (δ( 13 C) = 235.9 ppm (s, Ccarbene)), [( Me CAAC)2Au]Cl (δ( 13 C) = 250.9 ppm (s, Ccarbene)) and

Preparation of 3.
A solution of phenylthioisocyanate (27 mg, 200 μmol, 1 eq.) in toluene (2 mL) was added dropwise to a solution of 1 (194 mg, 200 μmol, 1 eq.) in toluene (2 mL) at room temperature. The resulting yellow solution was stirred for 1 h. The solvent was removed in vacuo and the residue triturated with nhexane (2 x 1 mL). After washing with -40 °C cold n-pentane (2 x 3 mL) and drying in vacuo the product was obtained as a bright yellow solid. Single crystals of 3 suitable for X-ray structure determination were obtained by gas diffusion of n-hexane into a solution of 3 in C6D6 at room temperature for 5 d.

Preparation of 4.
A solution of KHMDS (240 mg, 1.21 mmol, 1 eq.) in toluene (10 mL) was added in small portions to a solution of 2 (1.32 g, 1.21 mmol, 1 eq.) in toluene (40 mL) at room temperature, upon which the originally colorless solution turned bright yellow. The reaction mixture was stirred for 15 h, during which a thick yellow suspension formed. The suspension was centrifuged, the solid separated and washed with n-pentane (3 x 5 mL). After drying in vacuo the product was isolated as a light yellow solid. Crystals of 4 which were used for X-ray structure determination were obtained by gas diffusion of nhexane into THF-d8 at room temperature overnight. Although this allowed the determination of the connectivity (see Figure S78), no accurate structural parameters could be determined, due to the poor quality of the crystals. All other crystallization methods tested did not yield crystals of higher quality. Yield: 1.17 g (1.04 mmol, 86%); 1 H NMR (THF-d8, 303 K, 700 MHz, in ppm): δ = 7.14-7.10 (m, CHAr, 2 H), 6.99 (t, 3   moisture, a slight deviation in the value for carbon of 0.51% is recorded. We were not able to obtain better elemental analysis results for this compound.).

Deprotonation of 3.
A solution of KHMDS (26 mg, 130 µmol, 1 eq.) in toluene (2 mL) was added dropwise to a solution of 3 (144 mg, 130 µmol, 1 eq.) in toluene (4 mL) at room temperature, upon which the originally light yellow solution turned deep yellow. The reaction mixture was stirred for 17 h, after which all volatile components of the still clear solution were removed in vacuo. The residue was triturated and washed with n-hexane (3 x 2 mL) and dried in vacuo to give a deep yellow solid (133 mg, 89% of the theoretical yield of potassium salt of 3) which subsequently was analyzed by (VT) NMR spectroscopy (see Figures  S34 -S39). The results of this investigation indicated the presence of at least two isomers in solution (e.g. isomers A and B as shown in Figure S36), which interconvert into each other. This made a definite assignment of the crowded 1 H and 13 C resonances difficult ( Figures S34 and S35). Therefore, only the better separated 31 P resonances were tentatively assigned ( Figure S36). Repeated crystallization attempts under different conditions failed to produce suitable crystals for X-ray structure determination of either isomer in question. Elemental analyses of different batches were carried out repeatedly, and each time the elemental composition was found to fit well to the calculated composition of the potassium salt of 3, with only minor deviation (< 0.5%) in the value for carbon.

Preparation of 5.
To a mixture of 4 (113 mg, 100 μmol, 1 eq.) and (IPr)CuCl (49 mg, 100 μmol, 1 eq.) was added diethyl ether (4 mL) and the resulting suspension stirred for 1 h at room temperature. After removal of the colorless precipitate by centrifugation and filtration a light yellow solution was obtained. The solvent was removed in vacuo and the obtained solid recrystallized from n-pentane (1.5 mL) at -40 °C. After drying the microcrystalline material in vacuo the product was obtained as a light yellow solid. Single crystals of 5 suitable for X-ray structure determination were obtained by storing a concentrated solution of 5 in diethyl ether at room temperature. Yield: 123 mg (80 μmol, 80%); 1 H NMR (C6D6, 303 K, 700 MHz, in ppm): δ = 7.21 (t, 3

Preparation of 6.
To a mixture of 4 (89 mg, 79 μmol, 1 eq.) and (IPr)AuCl (49 mg, 79 μmol, 1 eq.) was added diethyl ether (4 mL) and the resulting suspension stirred for 1 h at room temperature. After removal of the colorless precipitate by centrifugation and filtration a light yellow solution was obtained. The solvent was removed in vacuo and the obtained solid washed with -40 °C cold n-pentane (2 x 4 mL). After drying in vacuo the product was obtained as a light yellow to peach-colored solid. Single crystals of 6 suitable for X-ray structure determination were obtained by storing a concentrated solution of 6 in diethyl ether at room temperature. Yield: 100 mg (60 μmol, 76%); 1 H NMR (C6D6, 303 K, 700 MHz, in ppm): δ = 7.21 (t, 3

Alternative One Pot Syntheses of 5 and 6.
To a mixture of 2 (113 mg, 100 μmol, 1 eq.) in diethyl ether (4 mL) was added solid KHMDS (20 mg, 100 µmol, 1 eq.), upon which the solution turned yellow. The reaction mixture was stirred for 30 min at room temperature, after which either (IPr)CuCl (49 mg, 100 μmol, 1 eq.) or (IPr)AuCl (62 mg, 100 µmol, 1 eq.) was added as a solid, respectively. After stirring for 1 h at room temperature, a sample of the respective reaction solution (0.6 mL) was transferred to a J Young NMR tube equipped with a sealed C6D6 capillary (for a lock signal) and a 31 P NMR spectrum was measured. In each case, full and smooth conversion to either complex 5 or 6 could be ascertained (see Figures S47and S55). Work-up procedures were applicable as described above.

Preparation of 7.
To a mixture of 4 (480 mg, 430 µmol, 1 eq.) and ( Me CAAC)CuCl (160 mg, 430 µmol, 1 eq.) was added diethyl ether (1 mL) and the resulting suspension stirred for 1 h at room temperature. The orange suspension was centrifuged and filtered. After all volatile components of the solution were removed in vacuo the light orange solid was dissolved in toluene (1 mL) and filtered. The filtrate was concentrated in vacuo to dryness and the remaining solid washed with n-hexane (2 x 1 mL). After drying in vacuo the product was obtained as a light peach-colored solid. Single crystals of 7 suitable for X-ray structure determination were obtained by slow evaporation of solvent from a concentrated toluene solution of 7 at room temperature.

Preparation of 8.
Route A: To a mixture of 4 (72 mg, 64 µmol, 1 eq.) and ( Me CAAC)AuCl (33 mg, 64 µmol, 1 eq.) was added diethyl ether (1 mL) and the resulting suspension stirred for 1 h at room temperature. The orange suspension was centrifuged and filtered. After all volatile components of the solution were removed in vacuo the light orange solid was dissolved in toluene (0.5 mL) and filtered. The filtrate was dried in vacuo and the remaining solid washed with n-hexane (2 x 1 mL). After drying in vacuo a light peach-colored solid was obtained. Repeated recrystallization and washing attempts to purify this raw product failed and no yield could be determined. However, NMR spectroscopy clearly showed that 8 is the main product of the reaction, since the 1 H NMR data are comparable to those of 7 (compare Figures S56 and S65) and the distinctive 13 C and 31 P resonances can be confidently assigned to the PN, phosphaureate and carbene ligands, in analogy to complexes 5 -7 (see Figures S66 and S67).

Route B:
To a mixture of 2 (54 mg, 49 µmol, 1 eq.) and ( Me CAAC)Au(HMDS) (32 mg, 49 µmol, 1 eq.) was added toluene (5 mL) and the resulting light yellow solution heated to 120 °C for 13 d. The progress of the reaction was checked regularly (every few days, see Figure 68) by 31 P{ 1 H} NMR spectroscopy of the reaction mixture to which a C6D6 capillary was added (for a lock signal). Although the desired complex 8 was found to be the main product, presumably due to decomposition during the prolonged heating, protonated ligand HPN had also formed in significant amounts. After cooling to room temperature, filtration and concentration of the filtrate to about 0.5 mL volume, only non-reacted ( Me CAAC)Au(HMDS) could be crystallized from the mixture. Several attempts to remove HPN by washing with -40 °C cold n-hexane or hexamethyldisiloxane (HMDSO) failed, since complex 8 also readily dissolved in these solvents. Attempts to crystallize the desired product 8 from concentrated toluene, n-hexane or HMDSO solutions at room temperature or -40 °C also failed.

X-ray Crystallography
Single crystals for X-ray diffraction experiments were measured at the analytical facility of the Paderborn University using a Bruker Smart AXS or a Bruker D8 Venture instrument. All crystals were kept at 130(2) K or 120(2) K throughout data collection. Data collection was performed using either the APEXIII or the Smart software package. Data refinement and reduction were performed with Bruker Saint (V8.34A). All structures were solved with SHELXT 7 and refined using the OLEX 2 software package. 8 All non-hydrogen atoms were refined anisotropically, and hydrogen atoms were included at the geometrically calculated positions and refined using a riding model. All structures have been submitted to the CCDC and can be obtained under the numbers presented in Table S1. For further crystallographic details regarding crystal measurements, please check Tables S1 and S2. The quality of the data obtained for 4 was very poor. Problems during the integration led to high Rint values and an incomplete dataset. Many atomic displacement parameters refine to negative values and R1 will not improve to less than about 25%. The model as such cannot be considered reliable. However, it matches well with other analytical means suggesting that at least the connectivity and overall conformation of the molecule are correctly described. Figure S1: 1

S85
179.23 (7) -----N100 -C100 -C101 109.3(2) ----- Figure S77: Thermal ellipsoid plot of ( Me CAAC)Au(HMDS). Thermal ellipsoids are shown at a probability level of 30%. Hydrogen atoms have been omitted for clarity. Figure S78: Section of the polymeric structure of 4 as obtained by X-ray diffraction analysis, showing the intra-and intermolecular interactions of the potassium ion with the P and O atoms as well as the phenyl and mesityl substituents of the phosphaureate ligands. Due the poor quality of the crystals, only the connectivity but no accurate structural parameters could be determined.