A-frame compounds

Uson and collaborators described an A-frame PdPt complex [C6F5Pd (p-C=N-p-tolyl)(p,-dppa)2PtC6F5] (75),85 and more recently, [XPd(p,-dppm)2 (p-C=N-R)Pt(CN-R)]+ (76-78) and [ClPd(p,-dppm)2(p,-C=N-R)PtCl] (79-81) were reported by Knorr and collaborators86-88 (Fig. 32). In the bis(isonitrile) heterobimetallics 76—78, a site selectivity in the second CNR ligand coordination (Pd vs. Pt) was noticed. The additional isocyanide is systematically coordinated on the Pt site.86,88 This distinct selectivity between Pd and Pt was explained by the greater lability of the Cl- ion on the Pt center as well as a better stabilization of the positive charge on the electron-rich Pt1 center.88 The question arises as to why the addition of ligand isocyanide sometimes produces the A-frame compound whereas under similar conditions, a d9-d9 isocyanide... 

The photophysical properties of the heterobimetallics A-frame compounds 77, 78, and 80 were investigated. The absorption spectrum of these compounds exhibit low energy bands in the 350—450 nm range, which are better resolved at 77 K. These broad bands are characteristic of an A-frame... 

With the tripod ligand np3 an entire series of compounds with tbp structures Ni(np3)X (X = Cl, Br, I, CN, CO, and H) can be prepared by reaction of nickel halides with the np3 ligand in the presence of borohydride, followed, if necessary, by metathesis with other X groups. The comproportionation of the Ni complex Ni2(CO)2(/i.-CO)(/i.-dppm)2 with NiG2(dppm)2 (dppm = Ph2PCH2PPh2) gives the iluxional A-frame compound (17-G-XIX).18... 

OC) ClRh(//-Ph2PCH2PPh2)2 RhCl(CO) reacts with nucleophiles, and as a result of reduction or thermal CO evolution forms interesting A-frame compounds (2.116). Similar compounds are formed by Ph2P(2-pyridyl). Phosphido... 

Analysis Our methods for making 1,2-dioxygenated compounds (frames 154-157) involve reductive linking of a dicarbonyl compound ... 

Another similar example concerns the alkylation of enamines. This reaction works well with reactive a-halocarbonyl compounds (frames 175ff) but simple alkyl hahdes often react on nitrogen ... 

The problem that we noted above with clusters appears also in chemical enumeration when we consider compounds formed by attaching radicals which may be chiral or achiral to a frame which is achiral. In this case, too, Polya s Theorem cannot be used, but the problem can be solved by the appropriate use of Burnside s Lemma. It is also amenable to the methods of Redfield, as shown in [DavRSl] and [LloE85]. 

The chiral information of stereogenic centers in the allyl moiety of the precursor is destroyed on deprotonation. While an i/3-bound ion pair with a planar carbon frame is a chiral compound, usually rapid racemization takes place by intra- or intermolecular migration of the cation from one face to the opposite one. The sole exceptions known at present are secondary 2-alkenyl carbamates with X = dialkylaminocarbonyloxy21, in which the cation is tied by the chelating ligand, see Section 1.3.3.3.1.2. 

The new arsino(phosphino)methanes with bulky substituents at the two donor centers can behave both as chelating and bridging ligands toward palladium(II). Besides neutral and mono- as well as di-nuclear cationic compounds, in which these ligands are bonded in a chelating fashion, a di-nuclear complex of the A-frame type could also be generated (see Scheme 5).396... 

Proof-of-efficacy trials these studies should provide, within a limited time frame and with a low-cost program, sufficient information for a go/no-go decision concerning efficacy and safety aspects of a new compound. The traditional approaches are Phase lib trials based on placebo-controlled dose-finding designs. These studies need relatively high power, which means the inclusion of several dozen to several hundred patients. 

A number of dppm complexes with hydride and methylene bridges have been referenced already in this chapter under the respective sections on hydrides and carbenes. These compounds will not be included again here. The binuclear platinum(I) chemistry of these complexes has also been developed. The complexes have a metal-metal bond between platinums, although this may be broken by formation of A-frame type molecules. This chemistry has been described in a series of papers, and the reaction types are outlined in Schemes 13 and 14, i28 .1438-1445 a similar chemistry will likely develop with the methylated ligand Me2PCH2PMe2.1450... 

Balch ei al. (306) have given a detailed report on novel A-frame-type methylene bridged palladium complexes of composition Pd2(dpm)2( p-CHR)X2 (X = I, Br, Cl R = H, CH3) and [Pd2(dpm)2(joi-CH2)L2]2+ (L = pyridine, methylisocyanide). It was demonstrated that the Pd—C (methylene) bond resists insertion of carbon monoxide, isocyanides, or sulfur dioxide. Protonation of Pd2(dpm)2(/x-CH2)I2 with fluoroboric acid yields the compound [Pd2(dpm)2(ju.-I)(CH3)I]BF4 in which the bridging methylene group of the precursor has been converted into a terminal methyl group, a process that has also been encountered in a previous example (52). 

Table I lists some properties of SMC and BMC. These are a function of resin composition, reinforcement, and molding conditions atid may be regarded as typical. This will serve as a frame of reference as to the property levels obtained with SMC and BMC. The differences which exist between SMC and BMC in tensile, flexural, and impact strengths are attributable to more than just the difference in glass loading. Fiber attrition arising from the compounding techniques for BMC as well as the shorter input fiber length account for the lower strengths.

It seems that (PhCH=CHPh)2, 2Na+ is also capable of existing in the polymeric form in a THF solution. This salt is a typical initiator in the polymerization of unsaturated compounds such as isoprene and methylstyrene. In THF such polymerization can include the detachment or fixation (chemisorption) of a framing (terminal) link from the polymeric aggregate [(PhCH=CHPh)2, 2Na+] . Methylstyrene captures the come-off link, starting the polymerization process. The link and, probably, [(PhCH=CHPh)2, 2Na+] i oligomer are included in a polymeric globule. The situation resembles a snake in a cage. In experiments (Podol sky and others 1982), a-methylstyrene was polymerized in THF upon the action of [(PhCH=CHPh)2, 2Na+] labeled with 3H, 14C in the presence of nonla-beled PhCH=CHPh. The authors obtained a polymer that contains the whole amount of the label. In the case of the mixture of nonlabeled [(PhCH=CHPh)2, 2Na+] with labeled PhCH=CHPh in THF, the polymer obtained did not contain any label. 

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