Here's is a trick I use to explain the meaning of dialectics. I will present the term using two methods: without, and with the dialectical approach. The second helps understanding dialectics better precisely by means of dialectics.
Method 1. Dialectics is a philosophical approach consisting in exposing the truth based on multiple perspectives. The longest answer in this question page includes a list of possible alternative descriptions, following the same line. This kind of exposition of ideas can also be called sentential or argumental, because a single simple sentence can be used to present the idea.
Method 2. Dialectics is to be understood as the opposite of argumental. An argumental exposition usually does not allow understanding the whole problem. The dialectical approach, on the contrary, presents ideas as the conclusion of a discussion considering the relevant issues of the subject.
In this last example, understanding the difference of argumental and dialectical allows an easy understanding of the term. Denoting such difference is precisely the goal of the dialectical method.
Same facts in a different form: a) dialectical is related to conclusions, argumental to propositions; b) dialectic is a discussion, argumental is an affirmation; c) dialectical considers all problems, argumental considers only one.
Regarding your question, "dialectical sentences" is an oxymoron, giving that "sentential" would oppose to "dialectical", as presented above.
Anyway, checking some Jameson's writings, it is clear that he uses a lot of sentence contrast connectors ("but", "nevertheless", "however", etc.), which can be understood as the simplest form of using the dialectical method. So, as a possible example:
The argumental method presents a single-sided perspective of things, HOWEVER , in order to expose relevant issues to consider, using the dialectical method is suggested.
Consider that the term dialectical applies to the method, not necessarily to a sentence. "Dialectical sentence" is possibly a Jameson's invention.