483We have discovered three curious features about the football-shaped molecules of the type below which make these aesthetically attractive species exceedingly interesting to study. One such feature is that the distance Z-E (YCH,CH,),N Z = R, SR, OR, NR,; E = group 4,14 element Y = 0, NR Z = lone pair; E = group 15 element Z = 0, NR; E = group 5,15 element Z = nothing; E = group 13 element Z = N; E = group 6 element between the ends of the football portion of these molecules can vary smoothly from the sum of the van der Waals radii of the atoms E and N, depicted as A, through intermediate distances, represented by B, to full transannular bonds, as shown in C. As will be (1) See, for example: (a) Tandura, S. N.; Voronkov, M. G.; Alekseev, N. V. Top. Curr. Chem. 1986,131,N. (b) Voronkov, M. G.; Dyakov, V. M.; Kirpichenko, S. V.

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Fourteen titanium alkoxides were synthesized for comparison of their catalytic properties in the bulk and solution polymerization of lactide (LA). In bulk polymerizations, they are effective catalysts in terms of polymer yield and molecular weight. Titanatranes gave polylactides with significantly increased molecular weight over more extended polymerization times, and those with five-membered rings afforded polymers in higher yields and with larger molecular weights than their six-membered ring counterparts. Steric hindrance of the rings was found to significantly affect polymer yields. Increased heterotactic-biased poly(rac-LA) was formed as the number of chlorine atoms increased in TiCl(x)(O-i-Pr)(4)(-)(x). In solution polymerizations, titanium alkoxides catalyzed controlled polymerizations of LA, and end group analysis demonstrated that an alkoxide substituent on the titanium atom acted as the initiator. That polymerization is controlled under our conditions was shown by the linearity of molecular weight versus conversion. A tendency toward formation of heterotactic-biased poly(rac-LA) was observed in the solution polymerizations. The rate of ring-opening polymerization (ROP) and the molecular weight of the polymers are greatly influenced by the substituents on the catalyst, as well as by factors such as the polymerization temperature, polymerization time, and concentration of monomer and catalyst.

The reaction of N(CH2CH2NHMe)3 with P(NMe2)3 or P(NMe2)2Cl yields the phosphatrane precursor N(CH2CH2NMe)2P,4. With oxydizing agents or electrophiles 4 is converted to the untransannulated four‐coordinated derivatives N(CH2CH2NMe)3PX, (X: O, S, Se, N3Ph, NPh, I CS2, 1/2 PtCl2). The structures of the compounds described are discussed by 1H, 13C, and 31P n.m.r. data.

The syntheses of MeN=P(MeNCH#H&N (4), [HRNP(MeNCH2CH2)3N](CF3C02) (R = Ph, S(CF3-C02); R = Me, 6(CF3C02)), [MePhNP(MeNCH2CH2)3N]I (7(I)), the stable azide adduct MeN3P(MeNCH2CH2)3N (S), and [HRNP(NMe2)3] (CF3C02) (R = Ph, 9(CF$02) are reported. Equilibria measured by 31P NMR spectroscopy reveal the relative ordering of basicity:The unusually strong basicities of the polycyclic cage bases (e.g., those of 1 and 4 are ca. 17 and more than 3 pKb units stronger than DBU, respectively) and the stability of adduct 8 is rationalized on the basis of partial transannulation from the bridgehead nitrogen to phosphorus which effectively delocalizes positive charge. The structure of S(CF3C02) determined by X-ray means is also reported, revealing a transannular distance of 2.559(4) A which is facilitated by a widened average MeN-P-NMe bond angle of 114.9(2)'.

The new titanatranes (Ar = 2,6-di-i-Pr-phenoxy; Ar‘ = 2,4-di-MeC6H2; x = 0, 5; x = 1, 6; x = 2, 7; x = 3, 8) featuring three six-membered chelating rings (5) to three five-membered chelating rings (8) in a stepwise fashion through 6 and 7 were synthesized from the corresponding trihydroxy chelating ligands 1−4, respectively, using an equimolar mixture of Ti(O-i-Pr)4 and 2,6-di-i-Pr-phenol. The molecular structures of 5 and 6, determined by X-ray means, revealed that in both of these complexes the transannular N−Ti bond lengths [2.305(2) Å, 5; 2.287(4) Å, 6] are at the short end of the range for titanatranes possessing three five-membered rings. These compounds show good catalytic activity for the bulk homopolymerization of l- and rac-lactide at 130 °C.

With concentrations as low as 0.0033 mol % ZPfMeNCHzCHz^N (Z = lone pair, 1) isocyanates are catalytically trimerized to perhydro-l,3,5-triazine-2,4,6-triones (isocyanurates) at room temperature. This reaction proceeds readily in the presence or absence of solvent, and the catalyst can be recycled at least six times without detectable degradation. Though not as potent a catalyst as 1, the molecule in which Z = NPh (3) also facilitates this reaction, and evidence is adduced that the catalytically active species is the adduct 3»ArNCO (6). In contrast, Ch=P(MeNCI^CH^N (Ch = 0, 4; Ch = S, 5) selectively catalyze the transformation of isocyanates to carbodiimides and do so more efficiently than their acyclic analogues 0=P(NMe2)a and (MeO)2P(S)Ph, respectively. The crystal structure of 4 is reported for the first time, and details of the crystal structure of [PhN=C(SMe)P(MeNCH2-CH2)3N]I reported earlier by us in preliminary form are presented. Both structures support the hypothesis that P-NM transannulation plays a lead role in the catalytic activities of 1 and 3-5.