The coordination chemistry of diselenoimidodiphosphinate ligands [SePR 2 NR 2 PSe] ร (1 a and 1 b) [1] has been extensively investigated. [2] In a series of recent articles, OBrien and coworkers demonstrated that metal complexes of the isopropyl derivative 1 b are suitable single-source precursors for the generation of thin semiconducting films such as MSe (M = Zn, Cd), [3] HgSe, [4] M 2 Se 3 (M = Ga, In), [5] PbSe, [6] Bi 2 Se 3 , [7] and CuInSe 2 , [8] as well as CdSe quantum dots. [9] The analogous tellurium-containing ligands were not available until recently when we described a new synthetic methodology that facilitated the generation of the phenyl derivative 1 c. [10] Since a reasonably high volatility is needed for metal complexes in CVD applications, we turned our attention to the synthesis of the isopropyl analogue 1 d, and its protonated precursor, 2. We report herein that the attempted synthesis of 2 unexpectedly produced the dimer 3, which can be viewed to result from the association of two tellurium-centered radicals [TePiPr 2 NiPr 2 PTe]C. The monotelluride 4 is obtained as the Pร H tautomer HPiPr 2 NiPr 2 PTe (4 a) rather than the N ร H tautomer 4 b.
The reaction of PiPr 2 NHiPr 2 P with one equivalent of tellurium in n-hexane at 23 8C produced 4 in 81 % yield. Complex 4 was characterized in solution by NMR spectroscopy and in the solid state by IR spectroscopy and an X-ray structural determination. [11] The NMR spectra indicated the preferential formation of the PรH tautomer 4 a; there was no indication of the presence of the NรH tautomer 4 b. The resonance for the PรH proton in the 1 H NMR spectrum appears as a doublet of doublets of multiplets located at d = 6.34 ppm, with a 1 J P,H coupling of 443 Hz, which is consistent with values reported for related systems. [13][14][15][16] In the 31 P{ 1 H} NMR spectrum, two mutually coupled signals for phosphorus are observed, one of which exhibits 125 Te satellites ( 1 J Te,P = 1654 Hz). In the proton-coupled 31 P NMR spectrum the other signal appears as a doublet ( 1 J P,H % 445 Hz) of multiplets. The solid-state IR spectrum of 4 a exhibits a sharp band at 2329 cm ร1 , which is in the middle of the range of values (2200-2460 cm ร1 ) reported for analogous compounds with a P V รH functionality. [13][14][15][16] The X-ray crystal structure (Figure 1) confirms the assignment of 4 a as the PรH tautomer. The PรH proton was located in the electron difference map and refined. The two PรN bond lengths are significantly different (P1รN1 1.622(2) versus P2รN1 1.589(2) ). The phosphorus-tellurium bond length of 2.3798(8) is similar to that observed in related compounds that contain a terminal P=Te bond. [17] The preferential formation of the PรH tautomer, 4 a, may be contrasted with the series of monochalcogenides